Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner

Reduced Engine Power Sensor

182K views 77 replies 40 participants last post by  chem_man 
#1 ·
The reduced engine power sensor on my 2003 Trailblazer keeps activating.
I have had it in the shop 5 times. Dealer has installed software updates, but
problem persists and is getting worse. They have no idea what is causing
this. Factory support has been no help. Looking for solutions.
 
#3 ·
Welcome to the site.

The "reduced engine power" message is not a sensor. It is a message from the PCM that some sensor(s) or operating parameters are not reporting correct information to the PCM or the sensor(s) are providing information that is causing the PCM to protect the powertrain. The problems that can cause a reduced engine power are probably too numerous to list.

Next time it happens, make sure you get the DTC codes and post them to the site. You should get many responses once you have some codes that everyone can make sense of. There are several very helpful members that can start to diagnose the problem with a little additional information.

I also agree with rcam81, fill out your profile so we all know what configuration you are driving.
 
#21 ·
Question for you

Yesterday I was driving and all of the sudden my cars slows to 10 mph so I let off the gas and all it did was Idle and when I gave it gas it dod nothing but rev up the RPM's. I had it checked out this morning and the codes that is pulling up are P1271 and P1635 also another code comes up as PO420 #1 and PO420 #2 (the #1 is talking about the oxygen sensor but that has been replaced). Do you have any ideas on what is going on with my Chevy? Any help you could provide would be great. Thank you so much for your time.
 
#4 ·
A friend of mine had his accelerator pedal sender-resistor gizmo fail and got the reduced power light. Replaced the pedal ass'y and that fixed it. I think it set a code so you might get that checked somewhere like AutoZone who will do it free. A stored code should lead you in the right direction.
 
#5 ·
My wife had this happen on the 06 5.3L and it turned out to be the throttle body and the ignition switch:confused:. Truck wouldn't go over 30MPH and the reduced engine power light was on. It definitely didnt protect the motor because right now it's in for a new long block.:worried:
 
#7 ·
Be it the pedal or the throttle body, it is about the same. The sender or the receiver, the signal did not reach it's destination. But, I do know the computer does not shut down engine power due to signal input. It only tells you the drivetrain is not functioning properly. +/- 7-10% expectancy.

How much money would GM make if they shut down an engine due to heat or oil pressure, or had the DIC tell you exactly which sensor or part went bad?:undecided
 
#8 ·
Reduced Power, engine light on

Just bought 2005 GM Buy Back loaded EXT with 25k on it. Immediately after brake controller was installed under dash, the reduced power thing happened with a check engine light on. Dealer found wiring harness under dash problem and fixed it.
 
#9 ·
Reduced Engine Power

I am looking for some assistance. My 2003 Trailblazer has 63,000 miles and has been experiencing the reduced engine power problem. A GM dealer has replaced a fuel sensor, entire wiring harness, computer, and it still is occurring. The only other thing they plan to try is the accelerator assembly.

Any thoughts on whether or not this should fix the problem??? I've been a very loyal GM owner, but this experience has me reconsidering that...
 
#10 ·
On whose dime are they doing that INSANE and EXCESSIVE amount of guessing? :eek:

What exact code shows up in the computer when it goes into REP mode and sets the SES light?

Typically the code will point to the throttle body or the accelerator pedal. There's a TSB that it might also be chafing in the wiring harness from the PCM to the fan clutch, or a failure in the fan clutch. We're very familiar with it here on trailvoy - hard to believe the dealer isn't.
 
#15 ·
Ggggrgrrr



I am having the same issue. Local mechanic said the code was the accelerator pedal. Put 2 aftermarket ones on and worked ok for about 3 weeks each time. Now the dealer says that they could put on a $380 GM pedal but no guarantee that it will fix the problem. (big surprise). Buy the way, the fan clutch sounds like a Tomcat ready for launch and that is another$800. Are these problems related? Seemed the Reduced Engine Power atrted back when I noticed the fan clutch starting to go out.
 
#11 ·
Like roadie said you really need to find out what the codes are setting the REP light.

I had this problem once and I ended up replacing the throttle body which was the most expensive thing i have had to do to my truck, but no more REP light.
 
#12 ·
Still having problem...

I have shelled out $1,200 for the fuel sensor, accelerator assembly, and wiring harness. The computer was covered under a warranty of some type. After the 4th trip where they replaced the accelerator assembly...it has been fine for the last 2 weeks...until today. Same problem....I won't pay Reeder Chevrolet another dime to fix this...taking it back tomorrow...any suggestions???:mad:
 
#17 ·
REP - will not start

First let me say thank you to all who have posted here. I'd been in lurk mode since before I even registered as a member, and never needed to post a question on account of the wealthy search.

My problem with the REP started a month ago on a hot afternoon after (coincidentally?) the truck had earlier run out of gas. GM service replaced the ignition switch. Next afternoon it got hot, driving in traffic, engine quits again. Then my old mechanic digs through the TSB's on it to trace it to some voltage problem, and thinking the sensor in the throttle is sending some faulty data back to the PCM, recommends replacing that. I put in a new throttle body myself yesterday.

After an hour of driving this morning, it quits again. What I have found gets me back on the road when stranded is to disconnect the battery cables, leave the hood up, and after it cools off 20-30 minutes its starts and runs fine.

So when I get it back home I find this thread on the fan clutch connector. So I disconnect that (5-wire @ top-right of radiator shroud?). It won't start. Cranks strong, no spark. Plug it back in, still no start. I got the codes (P0689; P2101; P0442; P1682). I left it sit there, an hour later came back, now it starts. With it running, same 4 codes + P1516 added.

Pulled off the connector again, no change. Other possibilities he had also suggested was bad battery cable, loose ground under fuse box... any other ideas? Way out of warranty, and the service guy @ GMC seemed to want to jump down the rabbit hole on my dime.

Scott
 
#19 ·
REP when hot

Judging by the "views", is this the second most common OEM concern?
Here's an update. Truck starts when cool. Disconnected fan clutch conn... still quits once it got too hot. In extreme temps (100+ weather) it may take a few hours before it will start again. As long as outside temp is <85 and I keep moving, it will run fine for hours until I hit traffic. Sometimes it will even make it to my destination if hot, but refuse to start again once it's turned off.

Plugged or unplugged, fan clutch seems to have no impact. It appears to only quit when I lift off the accelerator, like preparing for a turn or stop @ an intersection. I don't think it's ever done it with my foot on the gas. So it would seem to be a faulty voltage reading.

Anything besides battery/ground cable/fuse block I can look at diagnosing Monday when I can bring it in to somebody with the right tools? (see previous post for codes)

Replaced ignition switch and throttle body. Have NOT replaced APP or crankshaft sensor. Still original alternator/voltage reg.

It would seem to be something that only reacts to heat in the engine compartment. Similar to "TB shuts off when it gets hot" < http://forums.trailvoy.com/showthread.php?t=88932 > except it keeps going if cool enough outside.

The Roadie suggested having a scan tool connected when it dies. Easy enough to predict, if I can get somebody to go along with it. I'm just afraid of the dealer service dept insisting I jump down the rabbit hole to find it. I don't mind the process of elimination if the parts are cheap & I can do it myself. BTW - there's an ad post < http://classifieds.trailvoy.com/showproduct.php?product=4869&cat=2
> for a good throttle body if anybody else out there _actually_ needs one. :duh:

Thank you. I'm really sucking wind on this one...
Scott
 
#22 ·
REP and SES light

I am new to this post, just found it after researching my vehicle.

I just had a sensor replaced in the Gas Tank due to the recall (my gas gauge stopped working) And about (2) days later my vehicle starts having the Reduced engine power light, SES light and the stabillitrac light,

The codes popping up are P2135, P2138, and P0641. I had no problem with it prior to having the sensor in the tank replaced. I have 86,848 miles on the TB.
 
#25 ·
Ive been randomly getting the REP light, stabilitrak off light, and SES (code its throwing is p2138). A little while ago I had the headlight turning off issue and swapped the fan clutch relay with the headlight relay. Is there any possiblity that the bad headlight relay that is now in the fan clutch relay spot could be causing the REP and SES lights to come on? It only seems to be happening on days when it really hot out.

I've ordered a new relay already to replace the bad one, just waiting for it to arrive.
 
#28 ·
not overheating

I'm tellin' ya... that's the rabbit hole I went down for 3 months. It has to do with engine compartment temp more than water/engine temp. I drove around with the hood latch popped to increase airflow and keep the speeds around 35-45 when I could and that helped it do it less.

You are going to need to bring it to a shop you trust that is comfortable with electrical/ECM work. THey will be able to compare voltage irregularities between the fuse box on the engine side to the interior dash side to find where it is.
 
#29 ·
ECM/throttle sensor

ratlsnaktj, the ECM getting faulty info from the throttle control (code #2138) has to be a result from a shorted wire or cracked fuse box. It is not cooling system related. DO NOT bring it to the dealer... they will only have you replacing the gas pedal assembly and throttle body, which are not malfunctioning and will not fix the problem (I've got a brand new $375 throttle body here in a box if you don't believe me :duh: )

Now that the temps are cooling down, whatever plastic part that is the culprit is not heating up enough to expand and cause the break. The next hot day you are stuck in traffic it will do it again. The second you lift your foot off the gas, the fail-safe will misread voltage for throttle position and shut down the engine.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top