Engine Check Light on

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warren18
Posts: 2
Joined: Thu Jan 09, 2020 6:36 pm
Car: 1997 Nissan pickup truck 2 wheel drive 2.4 Ltr eng. auto trans

Engine Check Light on

Postby warren18 » Tue Jan 14, 2020 4:01 pm

I have a 1997 Nissan pick up truck with 130K miles. The problems started with the battery charge light dimly on. Then the engine check light came on. I started with the battery charge light being dimly on. I figured the alternator had gone bad even though the voltage at the battery with the engine running was 13.5 Volts. I checked the voltage at the Bulb check relay (yellow and black wire going into the relay). It was 9.6 volts. So I figured the alternator had gone bad. I bought a new alternator (not a rebuild). I still had the same problem. Again I checked the voltage at the battery with the engine running. Now I had 14.55 volts. I noticed the battery was old. And was a cheap battery. So I bought a new battery. The problem continued. Eventually I replace the bulb check relay after checking all the wiring to the charge light, including all the diodes in the instrument cluster and in the wiring harness attached to the large connector under the dash. All good. The new relay fixed the charge light problem even though the relay check out good out of the system.

But I still have the engine check light on. When I read the codes my scanner says there is 11 codes. When I clear the codes and restart the truck I don't get the engine check light on. On the second start up I get the engine check light on again with 11 or more codes. A few of the codes come and go. The truck runs fine. No indication of any issues when driving or idling. If I didn't live in CA, and didn't have to have the truck smog checked I would not worry about it. But I have to smog check the truck every two years. Does anybody have any ideas of whats going on? I appreciate any help.
Thanks


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Desert Rat
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Car: 2014 370Z M6 Base Coupe
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Re: Engine Check Light on

Postby Desert Rat » Wed Jan 29, 2020 12:56 pm

It should be OBDII. post up the actual codes. If you're making 14.5 volts at idle, your alternator is fine.

User avatar
Desert Rat
Posts: 1956
Joined: Wed Jan 17, 2007 11:57 am
Car: 2014 370Z M6 Base Coupe
2017 Frontier 4.0
2007 Dodge Ram 2500 Cummins Quad Cab 4x4
1977 F150 4x4 Shorty BUILT
2008 Boulevard C90T
Previous owner of a bunch of Nissans
Location: Mesa, AZ
Contact:

Re: Engine Check Light on

Postby Desert Rat » Wed Jan 29, 2020 1:00 pm

It should be OBDII. post up the actual codes. If you're making 14.5 volts at idle, your alternator is fine.

warren18
Posts: 2
Joined: Thu Jan 09, 2020 6:36 pm
Car: 1997 Nissan pickup truck 2 wheel drive 2.4 Ltr eng. auto trans

Re: Engine Check Light on

Postby warren18 » Wed Jan 29, 2020 6:14 pm

Yes thank you. The Alternator is new and with a new battery. Yes the Charging system is fine. Like I said the problem with the Charge light glowing dimly was the bulb check relay. I added that so other people with charging light issues can see what I chased down. A new relay fixed that problem ($17) .

Back to the ECU problem. After posting the first ECU questions, I printed out the ECU section of the service manuals pdf from this website. These are the best service manuals I have ever used. I with the help of these manuals I was able to check all the 118 pins on the ECU. The manual tells you what each pin should be reading electrically with a given condition of the Truck (Ignition on not running , Eng. running warmed up etc.). I found pins 115( O2 sensor heater) should be Battery voltage. It looked like it was floating around .9 vdc. And pin 52 the return for the rear O2 sensor heater should be 0 vdc . It was sitting a 2.4 vdc. Also pin 118 was incorrect. I checked the pin outs several times. Even on the first start up (never showing any codes) pin 115 and 118 and 52 still was incorrect. After reading the manual, after clearing the codes, the ECU will not turn on the engine Check light. Only on the second and following start ups will the ECU turn on the engine check light. I can't remember why they said why the do this. I did all this testing with my digital volt meter. You could also use a O scope if you have one. I do, but the DVM was easier. The ECU is now at a repair facility. The interesting thing was, all the other codes that were given, had all correct signals. And the rear O2 sensor code never did show up. But it was defiantly not right. The ECU repair facility confirmed I was correct. They also appreciated all the information I sent with the ECU so they could look directly at the problem. Just as a side note, the first pins I checked were all the 12vdc (battery voltage) and grounds connecting to the ECU. Those could make your ECU do weird things as well as a low battery voltage. When I get the ECU back I am going to change out the front and rear O2 sensors for good measure. Also I know O2 sensors output will change with age. Since the truck has a little over 130K miles on it, they are due to be changed anyway for the best performance.

This took quite a bit of time. But at least I knew the ECU was bad. I have had what looked like ECU problems before on other cars and after buying a new or refurbished ECU (several hundred dollars) the problem turned out to be something else. So I am very cautious when I suspect an ECU problem.

Thank for your help.


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