justmax

I installed a jumper in the ASCD (cruise control) relay spot sunday. The cruise control jumper worked perfectly, because the cruise control light was always on from the first second I started up the car after installing it. And I was able to operate the cruise control flawlessly.

Yesterday morning my MIL came on. "OK", I thought, "I'll just check the code, reset the ECU, and most likely the MIL won't come back". Well I printed out the instructions from the sticky post and this morning got down there to try it out.

BIG problem... the sticker on the ECU diagnostic test mode selector says "Idle Speed Adjust" on top. Around the circle, it has three labels:
near the bottom left - "low"
near the top left - "high"
near the top right - "self diagnostic"

So judging by the labels on the selector, I would not only be getting diagnostic codes, but depending on where the screw was originally, *I will be messing with the idle speed*!!!

Seriously, this screw is so hard to see, it would be impossible to get it back to whatever position it's currently in if I had to.

This is a '99 SE-Limited 5sp, so if anyone else has one and has successfully done an ECU diagnostic check, please let me know if your ECU has the same labels, did you have to hassle the idle speed, were you successful in getting the diagnostic code????

BTW maybe it was just a coincidence, but I put the ASCD relay back in. I'll go to work in awhile, but I don't think the MIL light can reset itself.

Thanks anyone for your help!!!

Justin

Daniel B. Martin

The Cruise Control "Always Ready" mod is mine. I installed in on my '99 GXE soon after taking delivery. The car has been my daily driver ever since (more than two years) and the MIL has never turned on. I believe this mod to be safe and effective. Other Maxima.Org owners have reported good results with this simple low-cost mod.

I have the '99 Maxima factory service manual. The instructions for resetting the MIL are given on page EC-65 and are in perfect agreement with the instructions given at http://vbxmaxima.8m.com/ecu.html per the Sticky ECU Diagnostic Trouble Codes.

Actually, it can. For further information, read the first post in the referenced Sticky which provides a simplified explanation of the MIL "turn on - turn off" logic.

justmax

Thanks Daniel. I do not doubt the correctness and completeness of the sticky nor the vbxmaxima web page. I believe that both of these references are in line with the info in the '99 Maxima FSM.

My problem is that the sticker on my ECU shows labels for an "idle speed adjust". Does this mean that all Maxima ECU's have this function built into the diagnostic selector, but most aren't labelled that way? OR does it mean that some models have an extra function built in and if I turn the selector screw, I'll be jacking with my idle speed?

BTW I read the first post and saw that the ECU can reset itself after 3 "closed loop mode" trips. I will go ahead and give that a try with the relay in.

Finally, 3 questions:
1. closed loop mode?
2. any idea whether all ECU selector screws have idle adjustment as a day job?
3. In the post about the ASCD relay jumper, I don't remember anything about wire guage, I used 12 guage, could that cause a problem?

Again, nothing at all seems to be wrong with the car, just the MIL 1 day after installing the jumper in place of the relay.

Thanks again for your help,
Justin

Daniel B. Martin

The Engine Control Module has two modes of operation called Open Loop and Closed Loop. Open Loop is used only until the engine is sufficently hot for the Oxygen Sensors to work, and then the ECM shifts to Closed Loop mode.

In Closed Loop mode there is a feedback loop.
The ECM causes the fuel injection system to go slightly rich.
As soon as the Oxygen Sensors say "Too Rich!" the ECM causes the fuel injection system to go slightly lean.
As soon as the Oxygen Sensors say "Too Lean!" the ECM causes the fuel injection system to go slightly rich.
This back-and-forth between lean and rich takes place about ten times per second. The consequence is that in Closed Loop mode the fuel mixture is almost perfect almost all the time.

I can't explain the legend on that sticker. The '99 Maxima factory service manual provides detailed instructions for adjusting the base idle on page EC-45 and it uses an adjusting screw on the throttle body, not on the Engine Control Module.

12 gauge is more than thick enough.

SighMax

iTrader: (1)

I looked at it the other day in order to check the error code and I also saw that idle adjust. Like you said, that thing is so hard to see. I ended up using my wife's small makeup mirror to get access to that tiny "phillips" and not a flathead. I have a 99SE by the way. The sticker on the driver's door said it the production year is 98.

I followed the direction on the web page and I haven't noticed any change in my idle speed. But I still havent gotten any response from anyone on what the code <b>0510</b> is. I've reset the ECU and the "service engine soon" light stayed off for few hours, but now it's back. Just waiting for my Y pipe to arrive. Hopely that's the only cause.

Daniel B. Martin

Diagnostic Trouble Code 0510 points to a problem with the Rear Heated Oxygen Sensor. This sensor is mounted in the exhaust stream, just downstream of the Catalytic Converter. When the two Front Heated Oxygen Sensors are operating properly the Rear Heated Oxygen Sensor is not used for engine control operation. It is used to monitor the condition of the Catalytic Converter. If either (or both) Front Sensors fail, the Engine Control Module uses the signal from the Rear Sensor to maintain a correct fuel/air mixture.

DTC 0510 is detected when the signal from the Rear Heated Oxygen Sensor does not reach the expected maximum voltage threshold value.
The possible causes include ...
- Harness or connectors (the sensor circuit is open or shorted.)
- Rear Heated Oxygen Sensor
- Fuel pressure
- Fuel injectors
- Intake air leaks

justmax

I'll go out and try it tomorrow morning (and I'm putting my ASCD jumper back in). Thanks for sharing your experience Sighmax, it's invaluable... and good luck with that rear O2 sensor. Daniel thanks again for the detailed info.

Justin