MIL on 2003 Sierra

[03Sierra17018]

Many time visitor, first time poster.... Hello, my 2003 Sierra has multiple codes stored... P0135, P0158 and P0160. It originally started as just P0160. It would stay on constantly even if cleared. But now I am getting 3 codes... I can clear the codes and they will stay off for up to 50 miles before coming back on, but then may also come back on immediately after clearing codes. Now I am also getting messages on message center for low battery for both FOB's. Replaced batteries, tried to reset, but still getting message. Not sure if I may have just O2 sensor and Fob issues or if it may be computer related. Any input would be appreciated. Thank you

[Coby7]

Sounds like you may have contact corrosion issues. Try cleaning your battery terminals and the fusible link. Maybe even re-seat all the fuses to clean them out. Just pull and re-insert.

[03Sierra17018]

Coby7... did what you said... key Fob issue went away. Drove truck to work 2 days, 30 mile round trip one way and check engine lite stayed off. Went to hardware store this morning and light came back on. Now codes P0134 and P0135. Never the same codes. Hate to replace all O2 sensors and still have problem. I even took O2 connectors apart and installed a little dielectric compound to the connectors.

[Coby7]

P0134 Oxygen Sensor Circuit No Activity Detected (Bank 1 Sensor 1)

P0135 Oxygen Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)

 

I don't think your HO² would have let go but connector may have fallen off if it wasn't properly secured.

 

Looks like some of the problems were solved. Now onto grounds. I believe there are 7 grounds under the hood alone. Rust and corrosion often get to these especially the ones on the frame. Clean one at a time so you know which one was the culprit.

[Coby7]

You very rarely get these 2 codes together unless you lose the ground because these codes would imply that the sensor and the heater let go at the same time. You got these codes because sensor one is the first to be tested by the ECM and it stops testing further down the line and set a code. Is your fuel gauge acting up because I think they have the same ground.....? But I'd have to check to verify.

[03Sierra17018]

Ok... so from the research i have done at https://www.gmupfitter.com/publicat/2004_BB/2003_Beyond_LD_Electric_CK.pdfpage B-15, it shows the following on the same ground:

PCM/ECM GND #1

PCM/ECM GND #2

PCM/ECM GND #3

PCM/ECM GND #4

TCM GND #1

TCM GND #2

NSBU SWITCH

MAF SENSOR & IAT

LOW OIL SWITCH

O2 SENSOR #1

O2 SENSOR #2

O2 SENSOR #3

O2 SENSOR #4.

Would I be having problems with all of these? Because I am not. And where would this ground be located?

[Coby7]

ECM will set a code for the first one tested, engine will run in open loop. Only thing you'll notice is it will probably be a little harder on fuel without the fuel trims. Follow the HO² harness it should lead you to the ground. Did you check all the fuses?

[rjgti]

measure voltage drop on battery cables also

[03Sierra17018]

ECM will set a code for the first one tested, engine will run in open loop. Only thing you'll notice is it will probably be a little harder on fuel without the fuel trims. Follow the HO² harness it should lead you to the ground. Did you check all the fuses?

I have looked for the grounds. I found the one and cleaned it. It shows the other ground on rear passenger side of engine block. I can't see that one, much less be able to get to it to clean it. I did find where a rodent has made a bed under the intake cover.. I hope I don't find chewed wires.

And yes I did check the fuses.

[03Sierra17018]

measure voltage drop on battery cables also

Ok. How do I do that?

[Coby7]

I did find where a rodent has made a bed under the intake cover.. I hope I don't find chewed wires.

 

Did you throw the nest away or take it apart to see if there were pieces of wire jacket. They don't eat the stuff they just rip it off to help build their bed. As far as fuses, I found it is not enough to just look, measure or beep them out. I prefer pulling them out checking them and re-seating them. That's when you find stuff like this. This one was pulled from a Cobalt BCM ECM/TCM fuse. Car had all kinds of problems like hard shifting, power steering, traction control and ABS. GMLan low speed communication goes through this fuse in particular. It was not inserted far enough and also the wrong value for that position.

 

[03Sierra17018]

Did you throw the nest away or take it apart to see if there were pieces of wire jacket. They don't eat the stuff they just rip it off to help build their bed. As far as fuses, I found it is not enough to just look, measure or beep them out. I prefer pulling them out checking them and re-seating them. That's when you find stuff like this. This one was pulled from a Cobalt BCM ECM/TCM fuse. Car had all kinds of problems like hard shifting, power steering, traction control and ABS. GMLan low speed communication goes through this fuse in particular. It was not inserted far enough and also the wrong value for that position.

 

 

 

 

So I checked the nest and it is only the insulation off the firewall. Also cleaned reseated all fuses. Found 2 for ECM were didcolored like they had gotten hot. Cleaned all fuses and reinstalled. Stayed off awhile but came back on. Also cleane main ground again. Not luck either. Had a former mechanic say that it has to do with cheap brand winter blend gasoline. Could that be an issue?

 

Also I noticed that you repair instrument clusters. My trucks gear shirt selector is only visible at night. I can not see it during the day. Any suggestions?

[Coby7]

 

Also I noticed that you repair instrument clusters. My trucks gear shift selector is only visible at night. I can not see it during the day. Any suggestions?

Yeah that's a problem with 03-05. Have you ever had your cluster apart? If you are comfortable with a small soldering iron I can guide you through it. You will need to reflow seven 510Ω resistors on the circuit board. You may need to add a little solder to accomplish this.