Service Engine Soon w/ Reduced Engine Power (code U1301, U1064, P1271) - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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OEM Issues Original Equipment Repairs and/or Problems

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  #1  
Old 09-09-2007, 05:36 PM
onip28's Avatar
onip28 onip28 is offline
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2003 Chevy TrailBlazer LS
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Question Service Engine Soon w/ Reduced Engine Power (code U1301, U1064, P1271)

Before posting I've scrolled around to see if anyone has had the same issues as I'm about to describe, and for the most part, the information thus far has been helpful; but there are unique instances for each and everyone of us so I'm wondering if anyone else can shed some light on my situation.

I got my 03' Chevy Trailblazer LS (4.2L V6 - approximately 52000 miles) about 2 months ago. I haven't had an issue with it until last week where I was driving and then the Service Engine Soon (SES) came on followed by the Reduced Engine Power (REP). As I read other posts, they could've move but 10mph, and at the time, I was on the autobahn in Germany, so you can imagine the speed in which I was driving versus other drivers...

I was able to get rid of the Reduced Engine Power by shutting of the TB and turning it back on, however, the SES light was still on. That eventually went away, only to come back on the next morning with the same problem - SES with the REP...(and yes, I checked the gas cap = OK)

Of course, I took it to get a diagnosed; pulled up these 3 codes:

U1301 - High voltage on the class 2 serial data circuit
U1064 - Body control module/loss of communication with DIM
P1271 - Accelerator pedal position (APP)/sensor 1-2 correlation

Asked a mechanic what these meant, and he simply said that the most important issue was code: P1271 and that I needed a new APP...

Now, the thing is, the SES nor the REP have come on since those two days last week.

The only time I see the SES on is when I turn the key half way in the ignition switch; I'm sure that's not suppose to stay lighted up correct???

My questions:

Should I proceed in replacing the APP?

Is that SES light suppose to be on when I turn the key half way on the ignition switch?

What do the other codes pulled up from the test mean: U1301 & U1064? Fixable?
---

My previous vehicles weren't technical as this one, so forgive me if I unload on all these questions...

Thanks to anyone and everyone that can shed some light on this.

Onip28
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  #2  
Old 09-09-2007, 06:59 PM
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I'll get you started with a few responses & questions...the check engine light will stay on with the engine off; this is considered a bulb check.

Once you start the engine, the light should go off unless you have a problem (which sounds like your case)

Do you have an aftermarket alarm or remote start in the vehicle? I ask b/c that combination of codes sounds like you may have spiked the OBDII line with excessive voltage a few times, and it is usually the result of aftermarket electronics

I would not get the accelerator until the concern is properly diagnosed...this code could indicate a fan clutch issue (spiking the 5V reference to battery voltage) or a wiring harness issue. both being addressed in different bulletins.
There is a good chance that all 3 codes are related It's unlikely that late model vehicles wind up with three separate, completely unrelated concerns at once.

Something else to keep in mind...OBDII codes do not condemn any parts without first performing the proper diagnostics on the system that it's referring to
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  #3  
Old 09-10-2007, 03:51 AM
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onip28 onip28 is offline
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Quote:
Originally Posted by PROSPHOTO View Post
I'll get you started with a few responses & questions...the check engine light will stay on with the engine off; this is considered a bulb check.

Once you start the engine, the light should go off unless you have a problem (which sounds like your case)

Do you have an aftermarket alarm or remote start in the vehicle? I ask b/c that combination of codes sounds like you may have spiked the OBDII line with excessive voltage a few times, and it is usually the result of aftermarket electronics

I would not get the accelerator until the concern is properly diagnosed...this code could indicate a fan clutch issue (spiking the 5V reference to battery voltage) or a wiring harness issue. both being addressed in different bulletins.
There is a good chance that all 3 codes are related It's unlikely that late model vehicles wind up with three separate, completely unrelated concerns at once.

Something else to keep in mind...OBDII codes do not condemn any parts without first performing the proper diagnostics on the system that it's referring to
Thank you for the response; no I don't have an aftermarket alarm nor a remote start, just the factory alarm that came with the vehicle. I haven't performed any mods as of yet so everything is standard...

And just to clarify, the SES light does go out when I start the engine - my concern was that it stays lighted when I turn the key half way from rest to actually starting the vehicle...I can't recall if that light is suppose to be on when I simply have the key turned half way, but the SES light does go off when the engine is completely started.

What other measures do you suggest I take in order to find out the proper diagnosis? I'll scope out other forums related to the fan clutch as I've heard this issue as well...but since this involves circuitry and wiring, I don't think I'll be tickering with this myself. Thanks for your help, will keep you posted...

Onip28
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  #4  
Old 09-10-2007, 08:38 AM
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onip28 onip28 is offline
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2003 Chevy TrailBlazer LS
Summit White 4.2L I6 2WD
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Quote:
Originally Posted by PROSPHOTO View Post
I'll get you started with a few responses & questions...the check engine light will stay on with the engine off; this is considered a bulb check.

Once you start the engine, the light should go off unless you have a problem (which sounds like your case)

Do you have an aftermarket alarm or remote start in the vehicle? I ask b/c that combination of codes sounds like you may have spiked the OBDII line with excessive voltage a few times, and it is usually the result of aftermarket electronics

I would not get the accelerator until the concern is properly diagnosed...this code could indicate a fan clutch issue (spiking the 5V reference to battery voltage) or a wiring harness issue. both being addressed in different bulletins.
There is a good chance that all 3 codes are related It's unlikely that late model vehicles wind up with three separate, completely unrelated concerns at once.

Something else to keep in mind...OBDII codes do not condemn any parts without first performing the proper diagnostics on the system that it's referring to

Could you elaborate more on what you mentioned in the bold/blue print above...I've looked around to see if this was an issue with anyone else, but haven't found anything that somewhat matches my situation.

I'll be on the lookout, thanks again.

Onip28
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  #5  
Old 09-10-2007, 08:53 AM
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Here's how the bulletin reads:

Quote:
Monitor the 5V reference to the Accelerator Pedal Position ( APP ) sensor, circuit 1274, using Peak Min/Max on a Fluke 87. Refer to Service information for the 5V reference schematics. Command the fan clutch control "on" with the Tech 2 at 50%. If when commanding the fan clutch on, the 5V reverence spikes to battery voltage, the concern is the 5V reference shorted to battery voltage intermittently inside cooling fan clutch. Replace the fan clutch to repair this concern.
The U1064 means that the BCM was not comunicating with the other modules in the vehicle, at least not the PCM...064 identifies he Body Control Module...have you lost function of any electronics in the truck in the past?

All symptoms considered, I would also be searching the engine bay, Instrument panel, and rear fuse block/wiring for a shorted wire or chaffed wiring harness
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  #6  
Old 09-10-2007, 09:43 AM
onip28's Avatar
onip28 onip28 is offline
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2003 Chevy TrailBlazer LS
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Quote:
Originally Posted by PROSPHOTO View Post
Here's how the bulletin reads:



The U1064 means that the BCM was not comunicating with the other modules in the vehicle, at least not the PCM...064 identifies he Body Control Module...have you lost function of any electronics in the truck in the past?

All symptoms considered, I would also be searching the engine bay, Instrument panel, and rear fuse block/wiring for a shorted wire or chaffed wiring harness
---

No, I haven't lost any functions with any electronics in the past; I just got this vehicle about 2 months ago used from a used dealer and had no prior historical problems...

My concern is the reoccuring problem; this just started to act up last week, Wednesday & Thursday (just once each day in the morning) and haven't occured since. I don't understand that, if there is an issue, then why is the SES light not currently on? I don't feel confortable having those DTC codes, knowing there is an issue with the TB.

I'll look into all the considerations you mentioned; I read other posts and I think I'll check the wire harness and the APP first thing and move from there...I greatly appreciate your help and I'll definitely you updated on the the progress...
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