2003 Maxima crank no start. Can't communicate with ecu
 

Let the car sit for a while. Old battery died. Replaced battery and now experiencing the following issues:

crank no start.
Can't communicate with ecu.
Car immobilized. Red light on solid.

Pulled ecu and opened it. No signs of damage. I can include pics if requested. Checked fuses under hood near battery. At a loss guys. Any help would be greatly appreciated.

Would you just replace ecu?

I wouldn't rush replacing the ECU.
It looks like your car has entered a NATS "Lock mode". This happens when you try to start operation five or more times consecutively with a key that the ECU does not recognize (this could be a caused by a bad key, or failure of the RFMD Rcvr on the steering column, or by a failure of the ECU itself).
To escape from the Lock mode:

1. Turn ignition switch OFF.
2. Turn ignition switch ON with a good key (previously registered with this ECU), but do NOT start the engine. Wait 5 seconds.
3. Return the key to OFF position.
4. Repeat steps 2 and 3 twice, for a total of three cycles.
5. Start the engine.

I tried to escape lock mode following the steps you outlined. Did not work. Still no power to ECU. Replaced ENG CONT 1 and 2 fuses just to eliminate a possible bad fuse. What other troubleshooting can I do?

Sometimes it helps to clear the codes, disconnect the battery for a minute or two then do the steps outlined. Should work out. Sometimes the code sticks around and still tires to immobilize the car.

The car has been unable to start to so I completely disconnect the battery after troubleshooting for the day. I don't get a CEL so I'm assuming no codes. Again issue is no power to ECU. Can't communicate with ECU.

Have you checked at the harness to see if it's getting power/has ground?

No how would I do that? Just to reiterate. I let my car sit since June and battery died. Replaced battery and car would not start. Immobilized can't communicate with ecu.

Unplug it from the ECU and test the leads in the connector.

https://cimg1.ibsrv.net/gimg/maxima....7a95ea82d5.png



I would also inspect as much wiring as possible under the dash and engine bay. Sitting that long invites mice to make themselves home and they're notorious for chewing wires.

Any specific leads I should check in the connector? Or test the ones indicated in your screenshot?

Red and black

How much voltage should they measure?

The black ones should be connected to Ground, and the Red ones to Battery Positive. So, when measuring the voltage differential against Ground, the black ones should show ZERO V, and the read ones should read ~ 12.5V (in real life, 11,5-14.5V.

And he must check continuity on the grounds.

I know this might sound like a dumb question but I'm new to troubleshooting electrical components and have yet to use a multimeter. It would be great if you could elaborate a little more regarding how to actually measure the voltage in this situation using a multimeter?

With the exception of the alternator, everything else on our cars employs Direct Current (DC) as opposed to Alternating Current (AC).
You want to measure Direct Current Volts, so you set m-Meter dial to "DC V" or the equivalent abbreviation on your meter (could be "=V" or something like that).
Then, you take the black probe of your m-Meter and attach/touch it to a suitable nearby ground. You take the other probe (red) and touch the pin you want to test. Read the voltage.

Oh, and you should check ground continuity as Child_ suggested. To do that, you check that the resistance between any two ground points on your car is zero, or something very close to it (a very small fraction of an Ohm at most). How to measure resistance .... should be obvious by now; if not, consult your m-Meter manual.

I'm not getting any ground continuity. I checked battery voltage is at 12.6V. With battery connected when I test for ground with negative prob on negative terminal and positive probe on multiple different ground points I get nothing. This is all with car off no key in ignition and battery hooked up.

Yes, you are (getting ground continuity) - your measurements indicate that there is continuity.
However, to measure continuity properly you should measure the resistance: Switch your m-Meter to resistance (indicated on the dial by "ohms", or Greek symbol for "Omega") and measure the resistance between"battery negative" and your test ground. The resistance should be zero (ideally) or only a very small fraction of an Ohm.

In either case, your initial measurements indicate that ground continuity is not a problem.

Maxiiiboy. I did do as you indicated and measured resistance by switching to ohms Greek symbol on multimeter and measured between"battery negative" and test ground. I got no reading.

do you have a spare key that's programmed to the car?

When you say "No reading" do you mean the same reading as when "the m-Meter probes are open (do not touch each other)" ? If so, there is indeed no continuity.

However, I am not sure this is going anywhere. Your problem is NATS-related. Your security light is on solid. You are either using a bad key, or your RFMD receiver in the steering column is not functioning, or your ECU lost its knowledge of your keys.

If you have any additional keys, try the "escape" procedure with each one of them. If not, you need to get your car to the dealer and have your keys re-programmed. This is the most likely cause of your problems. The other two possibilities - your ECU and/or your RFMD receiver being bad - are much less likely.

You are correct. When I say no reading. It is the same as if the multimeter probes are not touching each other. I only have one key and have been using the same key. Had locksmith come out to try and reprogram key and he tried 3 different computers and also could not communicate with ecu.

I am having the same or similar issues. How would one test the RMFD RCVR at the ignition switch. Also we have removed the ECU and its cover what signs should we be looking for to confirm it is not damaged.

If you can't communicate with the ecu, check the ecm relay.

We have Comm. as i am able to read and reset codes.