Hi folks,

I get the check engine light after the warmup and it goes closed loop. The standard paper clip in the code interface tells me that I have a code 13, which is an O2 Sensor. Being a good citizen, I had it replaced, and $85 later, I still have the engine light on, and code 13 reported.

I have disconnected the battery and after reconnection, checked and the code 13 is gone, but the drive to warm it up, brings the 13 back.

88 S10 Blazer with a transplanted 95 camaro 3.4l. The Sensor is the same part for it, and the original 2.8l,and the motor runs fine, but gets crappola mileage anymore, so its obvious the sensor is telling the engine to run rich, or so it would seem. Its a TBI, no FI.

Near as I can figure, the O2 sensor is a straight shot to the ECM, so the choices seem to be:

Bad ground, broken or shorted wire.

ECM is no good.

Got new sensor that is no good.

These will be easy to test, as I will also monitor the voltage at the sensor to make sure its moving between, I think .1 and 1.0 volts as the engine is warmed up. That should verify that the sensor is okay. Then check for the same through the harness to the ECM.

What I would like to ask is, are there other factors that can cause the code 13 to come up, even if the O2 is working fine? Being a TBI, I can't think of a bad injector running rich, and the TPS seems fine, but I do and will test it with the engine RPMs up around 2K.

Looking for ideas of where to go if I find that the O2 sensor is active, and the signal at the ECM is doing the same. I have never seen an ECM go bad on the older OBD1 systems, as there is not a lot of electronics in there, compared to the OBD2. It doesn't do that much, far as I know, so I am loathe to just replace it (about $60 at the junkyard) since I already lost a ton buying a new sensor.

Anyway, that said, what I seek is a direction to go in tomorrow, if the sensor to the ECM check out okay.

Any ideas, or experiences would be most appreciated.

Oh, I did search the forum for this issue, and there is a lot of sensor info, and its hard to find "code 13" so I hope no one minds if I revisit what may be found throughout the forum. Just not finding anything in the ton of data that comes up.

Thanks for your time and expertise,

John

 

You really need an oscilloscope to see the sensor trace from an O2 sensor. It'll fluctuate pretty fast. and the refresh rate on a digital multimeter may show a clipped signal which may not truly represent the signal.

I would measure the signal wire from the sensor to the ECM (purple wire cavity D7). Also check the resistance of the ground from the sensor body to a known good ground.

 

Thank you. I put a scope on it, and saw some oscillation, but the scary part was the amount of voltage the sensor was putting out.

I verified the connection from the sensor through the harness to the ECM, and made sure there was no short to ground.

Added a small connector so I could hang a voltmeter on the Sensor wire right at the ECM to observe it while I drove, and well, I am not sure why I saw what I saw. Maybe someone wiser than me can explain. :-)

When I start the engine from cold, the voltage off this new Bosch sensor, at the ECM, is 1.53 volts........ Waaay over spec. As it warms, it drops to 1.3 or so, and when it goes closed loop, it throws the engine light on, no kidding, 1.3V will do that :-)

Once I got the light, and saw the high voltage, pulled over, and shut the engine off, and the voltage rose back up towards 1.5V. That is a lot of voltage from an O2 sensor, if you ask me.

I have tested the grounding across the vehicle, battery, engine, and frame, and in a perfect world, its all zero ohms from point to point <g> but in my world, its 40-70 ohms from the engine to the frame, and several hundred ohms, between the battery and the frame. This is odd and hard to understand. All the grounds are either quite new, or were cleaned and bolted up tight when we installed the engine.

Regarding the O2 sensor, I read that the sensor goes into the harness, which gets its ground from the engine, which is in the 40 ohm range to the actual battery connection, so I don't think that is a big deal. Anyone disagree?

I even grabbed my jumper cables, attached them to the sensor housing, and to the battery ground, and it made no noticeable difference at the volt meter.

Again, the scope showed a waveform of about 5mv, but it was really going above or below that, and not a super scope, so accuracy is in question. The oscillation is riding atop the 1.5 Volts......

My shop manual says the sensor should live between 300mv and 600mv, sometimes as high as 1V, but anything beyond that will throw the code 13 which I have.

I will return to the muffler shop that put in the sensor, show them the meter connected and running at 1.3V but I think they are gonna plead the fifth, and tell me I have a problem somewhere else. Assuming I live through the process of beating them senseless, I still have the problem, and so I come seeking more wisdom and direction.

thanks again for your time,

John

 

I tested alot of things as well.Still Code 13. Did you happen to find any results?

 

All I found was that something in the wiring harness, or in one of the attached sensors, was blowing up the ECM. I replaced it and the same issue, 1.5V at the input line to the ECM for the O2 sensor.

At that point, I was stumped because there is now way to know which line is guilty, since there is no information on what to expect at each pin on the ECM. What I did was create a "breakout box" using connectors from the junkyard, which let me connect and disconnect each line individually. Trouble was, I got down to nothing connected to the ECM except power and ground, and I would still measure 1.5V at the O2 sensor input pin, with nothing connected to it. The ECM is generating that voltage at that pin.

Essentially, the truck eats ECM's <shrug> The solution would require a few more ECMs, at least, and connecting up each line one at a time until whatever line is the culprit, is plugged in, and causes the O2 input to rise to 1.5V. At that point the ECM is no good anymore, and another is needed, connect up the rest, and see what happens. Too expensive, too time consuming, and so two days ago, someone paid me all of $600 and drove it away. Being my daughter and son's truck, I explained the options, and neither wanted to put any more money into it <shrug> Problem solved :-)

I was very clear to the buyer about the problem, and told him in closed loop mode, the truck will run full rich, eat gas, and eventually self destruct, but he didn't care, gonna register it in a county that doesn't do emissions testing.

They were happy, I was bummed, and my daughter cried for half an hour because she loved that truck so much. Such is life when other things take priority over your wallet, like rent, insurance, etc.

I worked on cars when I was 13 years old, and this was the very first time that I lost, and failed to solve the problem, so my 42 year record is broken :-(

Good luck to all, and thanks so much for the help.

John

 

WOW. Sorry to here that. I'm at the same point. Haven't got any further with this on either. I just might part it out and say goodbye.

 

What symptoms do you have? Are you seeing what I have been seeing and dealing with.

We loved that truck. Daughter cried and cried when I told it was sold, but there comes a time when you reach that point of diminishing returns, and for us, that time came.

I usually live with the idea, "better the devil you know" and hang onto vehicles forever because if you want another one, you get someone else's pos,and have to start over piecing it back together, but it was their call as far as funding it. I would have gone ahead and torn out the harness, and rewired it, and tested and replaced all the sensors if they had wanted to put up the coin, but I am no position to fund it anymore, so someone got a pretty nice truck, with basically a brand new 3.4l engine, and some gorgeous wheels and new tires for a steal. More power to em <shrug>

John

 

I know how you feel. I have a new trans new 4.3 engine as well and it is a 4x4. I'd hate to seen go too but time is money and I would not like the idea of buying all those ecms to test it. I think i might break down and pull the harness out to check for grounded or broken wires. It's not going anywhere at the moment. I'll keep you posted.

 

I think what made me such an easy mark for my kids to say "forget it" was the notion of the harness being shorted, or open, or a sensor being bad. The problem with that scenario is, if any of those things was happening, or even if there was just a voltage out of spec, the ECM should throw another code, relative to whatever is out of spec, but I never got another code in months of driving it like that.

That tells me that something is very wrong, and I just wasn't gonna argue with my children when they decided enough was enough.

Would love to know what is was, but anything in the harness that is wrong, should give a code of some kind, on some sensor or input, or so I would think.

Good luck. I'm listening if you have an idea or get lucky and fix it up.

John

 

I think i might try one ecm and check the harness for breaks. I'm not sure if i clipped one while instaling the engine. It won't be an easy task but I feel i need to give it one more shot. I really like the truck.