GM Inside News Forum banner
1 - 11 of 11 Posts

·
Registered
Joined
·
64 Posts
Discussion Starter · #1 ·
Was driving along in my 2003 Chev Burb with my A/C running at low, when suddenly the DIC bings me as if a door were ajar, but displays the message HALF ENGINE POWER.:confused:

Pressed on the accelerator but the engine's rpm wouldn't exceed 1000, and the engine would shudder.

So I parked and popped the hood. Nothing visible wrong. No burning smell either. So after about a minute of looking it over, I tried restarting it. The engine came alive as though there were never an issue. Full power.

Anyone encounter a half engine power scenario, or know what causes it?
 

·
Banned
Joined
·
8,969 Posts
I had that happen to me- it has something to do with the throttle body. Basically it will not damage your truck but needs to be replaced ASAP or the truck will not work. If anything happens to your engine and throws a fault, the computer automatically puts the engine on reduced engine power so you don't blow it up- even if it won't harm it.

Bottom line- you'll have to take it in or have it towed to have it fixed.
 

·
Registered
Joined
·
64 Posts
Discussion Starter · #4 ·
Thanks for your inputs likarock and bouda.

I'll get it re-scanned. Previous scan indicated a faulty front knock sensor; pending to be replaced.

You figure it has something to do with the throttle body? Is there a service manual that refers to a reduced power situation?
 

·
Registered
Joined
·
1,222 Posts
The Trailblazers and related SUV's- with the I-6 (im guessing the V8 too) have a REDUCED ENGINE POWER light on the dash.
When this light comes on- engine power is reduced.
For the trailblazer- one of the main problems that causes this light to go on- is a bad accelerator pedal/sensor.
There is no cable from the pedal to the Throttle body.
instead the computer gets a value- think of it as a variable resistor-that changes based on how far youre pressing on the gas pedal.
press more- the value changes- and the computer knows you want more gas- and it then sends a signal to the throttle body to open more and for more gas to be supplied..........
But there comes times- when this sensor/resistor begins to fail.
so the computer commands a safe mode- reduced engine power.......
This is much better than having the computer not know where the pedal is- and commanding a full throttle operation-
 

·
Registered
Joined
·
64 Posts
Discussion Starter · #7 ·
The Trailblazers and related SUV's- with the I-6 (im guessing the V8 too) have a REDUCED ENGINE POWER light on the dash.
When this light comes on- engine power is reduced.
For the trailblazer- one of the main problems that causes this light to go on- is a bad accelerator pedal/sensor.
There is no cable from the pedal to the Throttle body.
instead the computer gets a value- think of it as a variable resistor-that changes based on how far youre pressing on the gas pedal.
press more- the value changes- and the computer knows you want more gas- and it then sends a signal to the throttle body to open more and for more gas to be supplied..........
But there comes times- when this sensor/resistor begins to fail.
so the computer commands a safe mode- reduced engine power.......
This is much better than having the computer not know where the pedal is- and commanding a full throttle operation-
So, in the case of a Trailblazer, is there a specific P code that identifies this pedal/sensor glitch?
 

·
Registered
Joined
·
1,222 Posts
GM ---P1271 Accelerator Pedal Position Sensor 1-2 Correlation


I also found this... though its for Trailblazers... but may give you a clue

Reduced Engine Power Message and/or Check Engine Light with any Combination of the following DTCs: P0107 P0112 P0122 P0452 P1120 P1220 P1221 P1271 P1275 P1280 P1481 P1515 P1540 P1633 P1635 P1639 P1682 #PIP3192 - (Oct 18, 2004)
Reduced Engine Power Message and/or Check Engine Light with any Combination of the Following DTCs: P0107 P0112 P0122 P0452 P1120 P1220 P1221 P1271 P1275 P1280 P1481 P1515 P1540 P1633 P1635 P1639 P1682 PCM Repeat
.

The following diagnosis might be helpful if the vehicle exhibits the symptom described in the PI.

Condition/Concern:
Reduced engine power message and/or check engine light with any combination of the following DTCs: P0107 P0112 P0122 P0452 P1120 P1220 P1221 P1271 P1275 P1280 P1481 P1515 P1540 P1633 P1635 P1639 P1682

Recommendation/Instructions:
If the SI diagnostics did not isolate a concern, the following information may be helpful:

Inspect the main engine wiring harness between the PCM and the generator assembly for a potential short to ground. There is a metal wiring harness retainer in this area that secures the main engine harness. If the harness conduit is mispositioned, some of the wiring may become exposed and chaff on the harness retainer. This may eventually cause the exposed circuit to short to ground.
Inspect the 3 harnesses that connect to the PCM for potential shorts to ground on the metal PCM mounting bracket, just below the PCM. There are plastic harness retainers on the PCM bracket that secure the harnesses to the PCM bracket. If the harness conduit is mispositioned, some of the wiring may become exposed and chaff on the PCM bracket. This may eventually cause the exposed circuit to short to ground.
If a chaffed circuit is found in either of the above locations, repair the circuit using the necessary SI procedures. Once the circuit is repaired, tape the area of the affected area of the harness to prevent the wires from becoming exposed in the future and secure the harness using the original harness retainer.

.



this applies to 04.

4.2 5.3 LL8 LM4 Engine with DTC - P2120 or P2122 or P2123 or P2125 or P2127 or P2128 - kw low MIL pedal power reduced #PI01746 - (Feb 17, 2004)
4.2 5.3 LL8 LM4 Engine with DTC - P2120 or P2122 or P2123 or P2125 or P2127 or P2128
.

When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.

Condition/Concern:
MIL light on. Reduced Power message on DIC. Possibles DTCs P2120 and/or P2122, P2123, P2127, and P2128.

Recommendation/Instructions:
The APP harness is clipped to the accelerator pedal bracket. The harness may chaff on the upper portion of the accelerator pedal causing a short to ground. Verify the harness is not chaffing on the accelerator pedal. After repairing the short, reposition the harness to ensure no contact between the harness and the accelerator pedal.
 

·
Registered
Joined
·
1 Posts
OK, 2003 TRAIL BLAZER.
DTC 1271... goes into reduced power mode.
Changed the app (accelerator pedal position) sensor assembly.
worked for a couple of weeks.
I was told to check the connector on the pedal for
'loose or poor" connection.
wokerd easter sunday for 60 miles.
failed the next morning.
read where the fan clutch could be shorting and puting a 12v spike on the 5v reference line to one of the sides of the APP causing a mismatched signal.
changed the fan clutch (costly)
sometimes it works for a day or 2 , then faults again...
another Chevy mechanic said there were electrical probs with that year, try running redundant 5v reference wires and redundant grounds..
did that ,,,, not the prob.
tried putting 5v reference #1 on both sides of the pedal, and tying additional low (-) wire to ground.
still no help..
what next?
I always get the p1271 code.
I can shut off the truck, then restart and it will run until the next time it sets...
I've tested the wires and the 5v ref's they all appeat to be fine.
I don't think it's the connector (10way f-150 plug at the pedal part # 15326842) but I have one ordered and will change it.
something else is going on, I don't see any evidence of chaffing or shorted wires, and the wires check out fine with an ohm meter and volt meter.
I'm at my wits end...
 

·
Registered
Joined
·
1 Posts
HI Tmkelly1,

did you ever solve your problem. Just curious as my 03 TB is doing the exact same thing since February 09 and I have done everything that you mentioned as well. I was just about to install a new clutch fan and saw your post. My TB seems to go into reduced power on steay throttle, light acceleration/low speed, and is more prone to do it after a cold start.
 
1 - 11 of 11 Posts
Top