NEED HELP 02 envoy rep

[Jrob21]

Envoy has the 4.2l and is throwing codes p1120 p1280 p0205 p0452 p1481 and is in reduced engine power. codes p1120 and p1280 do not clear when reset. Tested tps with multimeter, seems to be good... Hoping for a little guidance

 

[azswiss]

With multiple codes indicating fails for low voltage/reference low you might want to check for poor grounds (e.g. loose or corroded connections).

 

[Mooseman]

All the codes are unrelated to each other however p1481: Cooling Fan speed signal lost is a definite clue. The fan clutch can kill the throttle system. Unplug it, reset the codes and see if the codes disappear. Codes for the fan clutch will be there though. If that fixes it, replace the clutch.

 

[Jrob21]

I'll give it a shot and I'll update shortly

 

[Jrob21]

With multiple codes indicating fails for low voltage/reference low you might want to check for poor grounds (e.g. loose or corroded connections).

 

[Jrob21]

All the codes are unrelated to each other however p1481: Cooling Fan speed signal lost is a definite clue. The fan clutch can kill the throttle system. Unplug it, reset the codes and see if the codes disappear. Codes for the fan clutch will be there though. If that fixes it, replace the clutch.

Ok I cleared codes with fan clutch unplugged codes 1120 and 1280 did not clear. All others cleared

 

[Mooseman]

P1280 CHEVROLET Code - Accelerator Pedal Position Sensor 2 Circuit​

The pedal sensor actually has two sensors as a safeguard and if one of the two fails, it goes onto REP. The two sensors must match exactly. Unless you either connect two multi meters or use a scanner to check the two sensors and what the throttle body is giving in response, there is no way to know if both are working correctly. Because the code gives a problem with the circuit, you could check for proper continuity to each wire from the sensor to the PCM.

Because the PCM doesn't know which sensor is right, it doesn't know where the throttle should be and it also throws P1120.

As much as I hate the parts shotgun, I would throw a pedal sensor at it. If you have a pick-a-part yard, I'd grab a used one. While there, I would also grab a throttle body just in case. Just give it a shake test to be sure there aren't any loose bits inside.

 

[Jrob21]

P1280 CHEVROLET Code - Accelerator Pedal Position Sensor 2 Circuit​

The pedal sensor actually has two sensors as a safeguard and if one of the two fails, it goes onto REP. The two sensors must match exactly. Unless you either connect two multi meters or use a scanner to check the two sensors and what the throttle body is giving in response, there is no way to know if both are working correctly. Because the code gives a problem with the circuit, you could check for proper continuity to each wire from the sensor to the PCM.

Because the PCM doesn't know which sensor is right, it doesn't know where the throttle should be and it also throws P1120.

As much as I hate the parts shotgun, I would throw a pedal sensor at it. If you have a pick-a-part yard, I'd grab a used one. While there, I would also grab a throttle body just in case. Just give it a shake test to be sure there aren't any loose bits inside.

Would a pcm throttle body and pedal sensor from a 04 trailblazer be compatible to swap with my 02 envoy?

Thanks for the info and tims

 

[TJBaker57]

Keep in mind that if you swap a PCM it needs to come from a truck with the same gear ratio as your truck. There were 3 different ratios.

 

[Mooseman]

Would a pcm throttle body and pedal sensor from a 04 trailblazer be compatible to swap with my 02 envoy?

The PCM, as @TJBaker57 said, has to be the same gear ratio however, the year may also come into play. The 02 has an oil level sensor and no SAIS. The 04 didn't have the oil level sensor but did have SAIS. So my feeling is that the 04 PCM will not work in your 02. But right now, we don't have any reason to suspect it.

The pedal sensor, from what I gather from RockAuto, only 02-03 will work and from a the same wheel base as they mention if built at the Moraine OH plant (SWB) and Oklahoma City OK (LWB).

For the tb, I get conflicting info. Some part numbers say that only 02 will work but a couple others say 02-07.

 

[Jrob21]

So I am not getting enough power to throttle body. Tps 1 and 2 should have a 5v reading but it's only reading about .004v am I correct in assuming computer is bad and not regulating power to throttle body??

 

[TJBaker57]

Too early to tell. That power source is shared by many different systems. Best to try to isolate all the 5 volt sensor circuitry to find if one of the sensors or a bad wire somewhere is shorting that power to ground.

I read somewhere that these PCMs do not have protective circuitry for the two 5 volts power sources so it would be best to not leave the key on more than you must to check out the issue.

 

[Jrob21]

Thanks for the info I'll keep looking before I go fo a pcm swap.
I looked up the pcm number earlier while pricing them. The one in my envoy is numbered 16255757. I found that it is compatible for 2003 through 2006 I did not see it on the list for 2002 models. So that has me wondering if that's gonna be the culprit. Also any chance anyone has a diagram of the 5V circuits

 

[TJBaker57]

I don't know if there is a consolidated diagram of the 5 volt circuits by themselves. @Mooseman has service materials for download that will have all the diagrams. Off the top of my head I can rattle off some of the 5 volt sensors;

MAP sensor
Cooling fan speed sensor
Accelerator Pedal sensor #1
Accelerator pedal sensor #2
TPS sensor #1
TPS sensor #2
Fuel Tank Vapor Pressure sensor
A/C High Pressure Sensor


Did you test for 5 volts at both of the two TPS sensors??

 

[Jrob21]

I did same for both and thank you

 

[Mooseman]

The one in my envoy is numbered 16255757. I found that it is compatible for 2003 through 2006 I did not see it on the list for 2002 models.

2003-2005 sounds right however they may physically swap but the programming is different with changes year to year. For example, 2003 didn't have SAIS but 2004-05 did. They may physically swap however the programming is different with changes year to year.

Your 2002 is the unicorn as it has an oil level sensor and no SAIS, the only year with that combo. I think it may have already been swapped but unknown what year programming it has. If it's an 03, I think that would work but your oil level sensor would not work. 04-05 programming would not work since those would have programming for SAIS which you don't have.

2006 definitely not as it went to a totally different PCM.