Gen I code question

[jayriddle]

Hello,

Check Engine light came on in my '94, so I checked the codes using the ignition method (I don't have a code reader).

I get three codes in this order:

12 : This code is not listed in my Service Manual. What is it?
37 : Skip shift solenoid
21 : 02 sensor

I pulled both O2 sensors, and both check out at 5 ohms (normal).

If anybody here knows what code 12 is, and also why the car would show a code 21 with (evidently) working the O2 sensors, I'd be most appreciative.

Thanks in advance
Jay R.
Red '94, 88K miles

 

[grcforce327]

I think it's a code for battery disconnected(can't remember)!Checking ohms is a starting point,but isn't 100%.I've had bad solenoids that ohm good.

 

[Tom F&L GoR]

It could be that the 12 is the sign to start or end the code blinking.

In any case, ohms don't tell the story. How fast they react to exhaust gases does; the old OBD I won't even set the light unless it's several seconds in a row of poor performance. Mine both were bad but only rarely did the light come on. It wasn't until I borrowed a very good diagnostic tool that showed the O2 signal was way off, but not for long enough to light the light. Replaced both and it was a much better car.

 

[grcforce327]

I was right!Battery power disconnected or lost!

http://minimopar.knizefamily.net/fault/#11-17

 

[jayriddle]

Hi,

Thanks for that information. I haven't had any electrical or battery problems or disconnected the battery in a very long time. I've used a Battery Tender religiously since I last replaced the battery, and I've had no problems -- strong starts, normal reading on the alternator gauge, etc. But I haven't inspected my battery in several years -- maybe I'll pull the wheel and inspect it for corrosion.

The skip shift solenoid code was easily solved -- the lead clip had become disconnected.

As for the O2 sensors, I reinstalled them, and will leave the battery disconnected tonight to clear the codes. If the 21 code comes back, I'll replace the sensors regardless of the ohm-meter readings.

Thanks again for the suggestions.

Jay R.
Red '94

 

[RAYSIR]

Usually a code 12 is a pass code on system. Just means it is checking system. OHMs isn't a test for o2s. Use a digital voltmeter and backprobe the wire to computer after engine is warmed up and running at 2000 rpm. The voltage should switch rather fast between .1 v and 1.o volts but usually in the middle range bouncing hi-lo. The 02 produces voltage by chemical reaction of the exhaust to the platinum in the sensor. You can also read the voltage of the 02 with the 02 unhooked measuring its lead but then the computer will go rich and it will read(1.0V) because computer will see low volts and drive injectors open. Hope this helps.

 

[jayriddle]

Ray, thanks for the info. I must admit, reading your suggestions is testing the limits of my understanding of electronics.

Because I don't have a voltmeter, and I'm not sure I know how to backprobe, I'm going to stick with my original plan -- clear the codes and see if the removed, cleaned, & reinstalled 02 sensors trigger the 21 code again. If so, I'll plunk down the $180 for new brand new sensors. The car is 13 years old with over 88K miles and it's still using the factory-installed 02 sensors -- they can probably do with replacing regardless of whether or not they're still operating normally.

Thanks too for explaining the 12 code. I didn't find any problems with my battery, so I have a hunch you are correct -- the 12 code is just an indicator that the code-check process is initiating (like the 55 code at the end merely indicates "no more codes").

Thanks for the knowledge,
Jay R.