Hey guys, I posted another thread about a hot start problem and I am not getting much action there, so I thought I would post this since I think this will lead me to the problem. The car runs fine when cold (03, automatic) but after you turn it off when it's warm you cannot restart the car until it cools down. When the car is unable to start it will crank and crank all day but never start. When the car is unable to start the SES/CEL will not illuminate when the key is switched on. But once the car is cooled down the SES/CEL will function as it should and the car will fire right up. So I am wondering what sensors/module would be telling the car not to start and not to activate the SES/CEL? Thanks for any help.

 

The ECU pin 33 controls the SES light. I don't know a specific cause/fix, but maybe disconnecting the battery to reset the ECU might help. And before you re-connect the battery, remove the ECU connector and plug it back in.

Have you ever had a code reader connected to see if there are any pending codes?

 

I feel like something is getting hot and cutting either spark or fuel. I'll try the reset. It's a pain because the problem is intermittent and you have to drive it for a while before it will mess up.
The codes that I pulled are: p0420, p0430, and p1800

 

I don't know exactly what controls the SES light. As far as I know, that function is totally within the ECU. All the various sensors feed into the ECU, which looks at the voltage level and decides if it is good or not. But there is no sensor that controls the SES light specifically. Sensors that most commonly keep the car from starting are the crankshaft sensor and the camshaft sensors.

None of the codes you have would keep the car from starting.
P0420 is the bank 1 pre-cat and P0430 is the bank 2 pre-cat. If the pre-cats are truly bad, you do want to replace them. But right now, they could be false indications because of the no-start problem.

The P1800 is the VIAS control solenoid valve mounted on the intake manifold, passenger side. This similarly will not keep the car from starting.

When you read these codes, was it when the engine was running? I'm curious if the codes are reported when the car is warm and won't start.

Again, I don't know specifically what is wrong. Have you tried the ECU reset yet?

 

No I have not done an ecu reset yet. Something else that I posted in my other thread is that the owner of the car said you could hear a "click" then with in 2 seconds the car would be dead. No sputtering or anything. He also to me the problem was worse when the weather was hot out.

 

If the clicking is the fuel pump relay (seems like it's behind the kick panel on the driver side) turning off, could this cause the SES not to turn on if it's stuck in the "off" position? Futher more what could be getting hot that would tell the relay to kick off? I don't know that this is what's happening I am just guessing at this point.

 

I don't think that there are any parts external to the ECU that could cause the SES light to not come on. Excuse me, the light bulb could burn out.

There are several relays under the dash besides the fuel pump relay. Power window, ignition, blower motor, accessory are some of the others.

The ignition relay could prevent a car from starting, simple test is when the car won't start, see if the windshield wipers work. They also get their power through the ignition relay.

 

I'll try that, but would the car try to start if it was the ignition? The starter still spins fine the car just is not starting.

 

The starter circuit/wiring is not dependent on the ignition circuits or ECU, it will work.

 

Good to know. I have not had a chance to try anything yet, but I hope to have a little bit of time this evening. I personally have not witnessed the car dying with my own eyes so I have not been able to check anything out on my own yet. Thanks for the good suggestions so far.

 

Okay, I finally witnessed the car dying last night. When the car will not start the SES light will not come on when the key is switched on and the temp gauge does not register a temp. Also, something else I noticed when the key is switched on when it will not start the "AT check" light flashes 16 times then turns off. What does this mean? Under normal conditions this light comes on for a few seconds then goes off.

When the car will not start the wipers still work with the key switched on.

I inspected the cooling fans and the left/driver side fan was woobley on the fan shaft. This fan also would not turn on when the other fan turned on ~202* coolant temp. So I turned the a/c on to see if it would make the left fan turn on and it did not. So something is wrong with the left fan. Last night it was about 40*, when the functioning fan on the right would turn on it would run until the car was turned off or it would die. So the last time I monitored it ran for 30 minutes straight and never turned off. The fan came on around 202* coolant temp and while it was running the coolant temp would hover right around 195* and stay there until the car was turned off. Is the relay sticking open? If the cooling fan relay/circuit is messed up would that cause the car to be able to start? I am starting to think the cooling fan running too long is overloading the system some how.

Where is the ground/s for the cooling fan circuit? How about the relay? Could I pull the fan relay to see if I could replicate this problem while the car is cold?

*Another thought....is the AT check light flashing because the transmission is getting too hot? Since the diver side fan is not turning on this could also cause that side of the engine to be hotter. I have no clue what the AT check light is for.

 

The way the car is designed, when you go to start the car and first turn the key to the ON position (not START position), all the warning lights are supposed to light up as a light bulb test. If you don't start the car, most of them will go off after a few seconds.

Radiator fans - the driver's side radiator fan motor is bad. There should bed zero wobble in the blade. The bearings have gone bad and this extra play has destroyed the brushes. Replace the fan motor.

Without the a/c, fans should turn on at 203ºF so that part is OK. That it runs at 195º is also good. But the fact that the fan stays on for so long in this cool weather makes me wonder. Maybe its because of having only one fan. On my car, the fans start when the temp goes over 200º and run until the temp drops to 190º and that only takes a few minutes.

AT light - this light flashes when the transmission control module (TCM) thinks something is wrong with the transmission. And it is not from overheating because the radiator fan is burned out. First of all, check that the transmission oil is full. Low oil level will cause the light to flash. If that doesn't resolve the problem, run the self diagnostic on the transmission and see what the results are. Click on the link and go to page 53 and follow the directions.

transmission test - http://boredmder.com/FSMs/Nissan/Maxima/2003/AT.pdf

 

Thanks for all of the good information, I will check out the fam shortly. I ordered a new set of cooling fans, they should be here later this week. Also I had my dad check the transmission fluid, he did not tell me if it is low but he did say it is a light brown color, so I am going to change that fluid and possibly add a tranny cooler as well. With the AT check light flashing will that cause the car not to start?

 

The AT check light will not prevent the car from starting.

Auto trans fluid can be a brown color. The red is just a dye to identify it. Some say it was so you could tell if it was ATF or engine oil dripping on the ground. But times have changed and ATF isn't always bright red anymore. If you want to get the oil changed, go ahead. You are supposed to change the transmission oil anyway.

Adding a transmission oil cooler is rarely needed. There is one on the car already. It's not the greatest, but unless you are road racing and constantly shifting, it could be beneficial. For normal driving, it won't make a difference.

 

I changed the cooling fans tonight, and now they both come on with the a/c then they also both come on at 203* and turn off at 190*. I let the car idle for a while. The first two times the cooling fans came on they ran for about 2 minutes and turned off. I was monitoring the coolant temp, and they came on at 203* and turned off at 190*. The third time the cooling fans came on at 203* they ran for at least 10 minutes and never got the coolant temp below 192*. Not sure if the engine was heat soaked at this point or what. Is this normal? I ran out of time so I could not let it run any longer but it did not seem that it was going to take it below 192*.

I also cleaned the ground from the battery that goes to the block (via bracket). That was soaked in oil so I figured it could not help.

I also drained and refilled the transmission fluid. According to how much I drained and how much I put back in I think I was around a quart and a half low on transmission fluid. No the fluid is the proper color and at the proper level.

I also changed out the VIAS solenoid, with another used one.

I let the car idle for about 45 minutes and I could not get the car to die...not sure if anything is fixed or not, but I could not recreate the problem I was having before.

I still am curious would would cause the car not to start. I am guessing since the SES does not come on the ecu is killing everything. Can the BCM tell the car not to start? I want to know what is telling the car not to start.

 

The BCM is a 4th gen part. It was re-designed for the 5th gen and is called SECU, Smart Entrance Control Unit. It probably could prevent the car from starting in an indirect way as it does send signals to the ECU. The vehicle alarm portion of the SECU will directly prevent the engine from cranking over, but this is not the problem that you are having.

If you want to clean a ground, clean the main ground point for the battery to the chassis. It is right next to the battery. Follow the Neg cable down from the battery.

 

Any ideas on why the cooling fans would run for half an hour and the coolant temp would only get down to 192? The first two cooling fan cycles only lasted about two minutes each. They cut on at 203* and turned off at 190* The third time they came on they cut on at 203* and got the coolant temp down to 192* and then stayed there until I tuned the car off. It was idling the whole time it was running.

I assume the fans are given 12 volts when turned on, and they spin at a certian speed with 12 volts. Could I be having a voltage drop not causing the fans to spin fast enough therefore not cooling the car efficiently?? Just brain storming here. If this is the case what could cause this?

 

Specifications say the fans should kick on at low speed when coolant temperature reaches
95C/203ºF. But I have not seen a spec for when they should turn off. My car turns off at around 190ºF.

Exact numbers need to be taken with a grain of salt as you have production tolerances in the components such as the ECTS.

However the fans should turn off. I don't believe heat soak is a factor or even happening, especially at this time of the year. We have warmer summers here where I live and the fans work the way you would expect even on 105-110º days.

Maybe the thermostat is not opening up all the way and not allowing enough water to flow. The only way to test for this is to take it out of the car and but it in heated water, monitoring the temperature and how much the thermostat opens. Then compare that to what is in the FSM. One thing is that Nissan's seem to have problems with aftermarket thermostats.

 

Yeah, that's the other thing I was thinking it could possibly be. Either the thermostat was not working correctly or the radiator might not be flowing up to spec. I think rather than testing the thermostat I would rather just throw a new one in it, then go from there.

 

UPDATE: Car still has the problem

I changed the thermostat with a nissan thermostat. No when the fans come on they only run for about a minute and then turn off...I let the fans cycle about 10 times and they preformed this way every time so I was happy that that was fixed.....but as soon as I turned the car off the car went back to the SES light not working and the AT light flashing 16 times and the car would not start. A few things that I verified while it was not starting. I could not connect to the ECU via the OBDII port via the OBDII scanner, and also the fuel pump is not priming when the key is switched on. So something is taking the computer out of the loop.

While the car was not starting I go my brother and dad to help me so that I could listen in the engine bay, because when the car does not start you can hear a buzzing noise in the engine bay when you switch the key "on". If the car makes this buzzing noise it will not start. I have not pinpointed where the noise is coming from but it sounds like it is coming from the transmission area. I took a video of the buzzing noise when the key is being switched on. If you would like to see it please PM me and I will text it to you.

So once the car cooled down (while I was working on the car it was about 35 degrees outside) with the hood open for about 10 minutes it would start right up like nothing was wrong. So I tried to replicate the problem I was having with out the car getting hot. What I found is that if I unplugged the "Engine Control" relay in the relay box behind the left headlight I could cause the same problem. The AT light would flash and the SES light would not turn on and the car would not start. That's where I am at this point. I think I am on to something but I still have the problem. What is tied in to the Engine Control Relay? Anything on the transmission? Any ideas on what could be causing this? Does anyone have the wiring schematic for wires going to this relay?

 

That relay connects power (battery voltage) to a bunch of things that could keep the car from starting. They are: the ignition coils, both camshaft position sensors, the crankshaft position sensor and the MAF. It also sends power to the ECM (also called the ECU) on pins 110 & 112. The ECM/ECU probably relays that power to other things as well as utilize the power itself, but I don't have any documentation of what goes on inside the ECM/ECU.

That relay itself is energized by the ECM/ECU. What you could do is swap the relay with any similar colored relay and see what happens. I would recommend using RAD FAN 1 relay as we know that one works.

That buzzing noise could be coming from the ABS unit. Maybe 2 months ago there was someone who was having a buzzing sound in that area and it turned out to be the ABS. But how that figures into your problem, once again I don't know.

There are 3 connections between the ECU and the TCM: the tachometer signal, the accelerator pedal position sensor and an unnamed signal between TCM pin 41 and ECU pin 72. If the ECM relay is not sending power to the ECM/ECU, the TCM is not getting signals from the ECM/ECU and says something is wrong.

If you want the electrical wiring diagrams, you can download the FSM from here:
http://boredmder.com/FSMs/Nissan/Maxima/

Section EC (engine control) page 28 is a diagram that shows the Engine Control relay. You will find that section IDX is helpful, it is the alphabetical index for the manual. There is a learning curve to using this manual. I would recommend reading section GI (general information) as it explains how to interpret the manual.

 

If it was one of the sensors that receive their power from the engine control relay, would it cause all of these problems? For example: if one of the cam sensors is bad then would that cause me to loose the connection to the ecu? Would it cause the temp gauge in the car not to work? Is it likely that the relay could just be bad? It seems to me that if just one sensor is having an issue it would not cause a disconnect from the ecu. I'm just trying to talk it out.

 

got it to fail again today and I swapped the engine control relay with the Rad Fan 1 relay...no change. So I don't think it's a relay problem. I need to look at the wiring diagrams.

 

I read a thread from a few years back that Shift Max was having a problem with the car not starting and he was not able to connect to the ecu via the OBDII port. His problem turned out to be either cam or crank sensors, I think he replaced all of them. These sensors have been replace on this 03 maxima and the problem persists, but they were also replaced before I fixed the thermostat/cooling problems going on, so maybe something got cooked???

One thing that puzzles me is that if a failing cam or crank sensor can cause the disconnect from the ecu why can I not replicate it by unplugging the sensors? I tried unplugging them one at a time and the SES light still illuminates...


*eidit* Maybe next time it fails I will try unplugging sensors one at a time to see if that allows the ECU to get power...huummm

 

The cam and crankshaft sensors do not send power to the ECU. The sensors do send a signal to the ECU that is used for ignition timing, but these signals do not power the ECU.

As an experiment, swap the ignition relay. It is located inside the car, on the backside of the fuse panel. There are 3 relays. The ignition relay is different from the other 2. It is the same as the radiator fan and engine control relay. I really don't think this is it, but this relay can cause some of the symptoms.

 

I have not had a chance to work on the car any more, but now the car is at my house so I will have easier access to it, so hopefully I can get somewhere. It was driven 20 miles to my house and it ran fine. But while it was sitting in a parking lot idling for about 10 minutes it cut off....no sputtering or anything....just cut off. Poped the hood to let it cool off, and it fired back up after 10 minutes of cooling down and then was driven all the way to my house with no problems.

 

Hey guys, here is a video, of a buzzing noise from under the hood when the car will not start. Once the car will start after cooling down this buzzing noise does not happen. I cannot figure out where it is coming from. Any ideas?

 

That's a video I posted above, you have to click on it to play it. Bump for new ideas?

 

does this mean that to disable the SES light all you have to do is prevent this pin from connecting? Or will it foul something else up?

 

still trying to figure this out

 

The ECU acts like a switch to light up the SES light. If you disconnect this wire, the SES light will never light. Disconnecting the wire won't solve any problem, all it does is keep the light bulb from light up. If you are considering doing something like this, I would just take the light bulb out of the instrument cluster.

I don't know what the buzz is. If you have an auto trans, it could be the motor mounts. You need to find out what is buzzing. This will probably point in the direction of the problem.

In regards to an OBD scanner not connecting, I don't see how cam or crank sensors would cause it. The ECU stores the codes in memory and so the car does not have to be running to read codes. The ignition switch has to be on, which sends 12 volts to one of the pins in the OBD connector which tells the scanner there is a car attached. Even if the voltage is there, other problems could keep the scanned and ECU from syncing up.

 

okay guys, how about some new ideas on this. I am ready to work on this car and I want it out of my garage. I tried swapping the rear cam sensor and harness and the crank sensor and harness with parts I got from the junkyard. No change. The car idled for 30 minutes then turned it self off and would not restart for about 30 minutes. When I switch the key on to start the car when it will not start the SES light does not come on, and the AT Check light flashes. When the car has cooled down and will start the SES light works and the AT Check light does not flash continuously at me. Can the TCM cause the car not to start? Any new ideas guys?

 

Have you looked at the fuel pump itself? It could be wearing out and overheating till it shuts down. The cool off period for the car would also allow the pump to cool off.

Next time you get it to fail, listen for the fuel pump to spin up when you first turn the key to the "on" position.

 

I have not really looked at the fuel pump. I have dealt with cars with bad fuel pumps before and they would not cause the CEL not to come on. Does the fuel pump get it's signal from the ECU? I think something is causing the power to be cut to the ECU...I just don't know what it is getting a signal from telling it not to work. That's just my guess right now.

I was googling yesterday and it seemed that a Subaru guy had a problem with the CEL not illuminating and it turned out to be a melted O2 sensor, I next time it fails I am going to try unplugging the O2 sensors one at a time. I know it's a shot in the dark but I am running out of ideas.

 

anyone at all?

 

I worked on this a little over the weekend. Here is some stuff I found out. When I unplug the sensor behind the transmission range sensor the buzzing noise I posted about in post #27 of this thread goes away but the car will still not start. After the car cooled down enough to start I tried cranking it with this sensor unplugged and it started up just fine, so I don't think the buzzing is related to not starting.

When the car was not able to start (no CEL present) I went around and unplugged all of the O2 sensors one at a time, this made no change, I also unplugged the electric motor mount and this made no change as well.

The path that I think I need to go down is this one. I pulled the engine control relay from the relay box behind the driverside head light. When the car was in good starting shape I got the following readings on my the terminals of the relay:

12.4 12.4
0 .5
12.4 0

Then while the car was exhibiting it's no start/no CEL condition I got the following reading on the same relay terminals:

12.4 1.65
0 .5
1.52 0


I am going to go try to find this stuff in the FSM but does anyone know where these wires come from to this relay? The two that I am very curious about are the top right and bottom left, the two that lost a ton of voltage when the car is not able to start or display a CEL.


Here is a link to the FSM where I am trying to figure this out http://www.nicoclub.com/FSM/Maxima/2003/ec.pdf

Start on page 28. I think the relay I am looking for is the one that is labeled "EMC Relay" on page 28. If I am reading this correctly it looks like the bottom left leg on the relay should be coming from the battery going though a fuse or fusable link and then to the relay. Then the top right leg is going to position 38 on the ecu.

 

I don't have a pin out for the ecu, does anyone know if pin 38 is where the ecu is supposed to receive 12volts from the relay?

I am not an expert in wiring by any means, and this relay is a little more complex then relays that I have bypasses in the past. Am I able to wire this with out the relay to force it to work. I.e. taking voltage from the terminal that still shows 12v when the car is failing and then tie it into the others that show battery voltage when the car is running fine?

 

I did some more testing today and found out my fuel gauge does not work when I ran out of gas. Is there anything on the fuel pump that can tell the ecu not to work?

Also I probbed the eng control relay agin while the engine was running and these are the reading I got.

12 12
12 12
12 .9

Then when the car failed I probbed the back of the relay while it was plugged in and these are the reading I got:

12 .41
.01 1.32
.4 .4

So what the heck is going on?

The two pins closest to the top on the right (.41 and 1.32 readings) are supposed to be going straight to the battery if I am reading the wiring diagram correctly. Can someone please double check this for me? I am not good at wiring if no one has figured this out yet. But I am wondering if I can make a new fused line coming off the battery and run them straight to the two pins referenced above the top two on the right? Would that hurt anything? When I follow those two wires even though they are shown as short little runs to the battery they go into some loom and go under the upper radiator support to the other side of the car.

Please help

 

The engine control relay as it is labeled on the cover is called the ECM relay in the service manual. One of the many quirks in the nissan documentation.

Regarding ECU pin 38 (post 37) - pin 38 is not receiving voltage on this pin. The ECU energizes the ECM (or engine control) relay with pin 38. The ECU internally connects pin 38 to ground. In the 2003 Nissan FSM, look in section EC, page 156 and you will see the schematic for the ECM relay.

In the voltage readings that you posted above, I need to know the pin numbers they represent. Look closely at either the relay socket or the bottom of the relay itself for the pin numbers. If you are looking at the bottom of the relay, remember that holding the relay up side down flips left and right. You can also get the pin numbers from the FSM. Section EL (ELectrical) has the socket arrangements on page 10. The ECM relay is the 2nd one down.

But looking at the schematic on page EC-156, you will see that three of the relay pins (2, 3 and 5) are supposed to have 12 volts from the battery on them. And this is all the time, whether running or not. And when the relay is energized, it is passing 12 through a pair of contacts to pins 5 and 7 which is powering the ECU via ECU pins 31 and 110. The 6th pin on the relay, pin that connects to ECU pin 38, will close to zero when the relay is energized. When I say close to zero, Nissan says less than 1 volt. If the relay isn't energized, then relay pin 1/ECU pin 38 will be towards 12 volts on a good working car.

Looking at the wiring diagram and looking at your voltage readings, I am wondering if you are having a problem with either the fuse that supplies 12 volts to relay pins 2 and 3 or wiring connections between these points. I'm referring to fuse # 59 in the schematic, the right most fuse.

This fuse is located in the fuse panel that is between the battery and the fender. The cover for this fuse is labeled "ENG CONT 2".

I remember someone that was having a problem with their headlights and they tracked it back to this fuse panel. Underneath it were screws that had come loose that held some kind of electrical connections together. These metal bars evidently brought the battery voltage to the fuses. This was a couple of years back and this is the best I can recall it.

FWIW, if you want to know what is on an ECU pin, look in section EC, page 141.

 

Where I posted above with the voltage reading here are the pin numbers according the the relay and the diagram in the FSM

3 6
5 7
1 2

Does this point to anything? I bought some alligator clips today so I can do some testing. Is there a way I can force voltage where it should be?


** for example, can I try running 12volts to pin numbers 5 and 7 on the relay since they show going to the battery according to the wiring diagram assuming I am reading it correctly**