Reduced Engine Power

Steadicam305 · Monday at 1:09 PM

I own a 2004 Suburban 8.1L 2500 LT 4x4. More than often I'm getting a "Reduced Engine Power" message in the dash & starts mis-firing badly.

I shut it off. Lock the car. Unlock it. Fire it back up & it all goes away. No mis-firing or "Reduced Engine Power" message.

What could this be?

99Sierra2500 · Monday at 3:06 PM

I would look at the diagnostic section of the shop manual here: https://lemon-manuals.la/Chevrolet/2004/

Steadicam305 · Monday at 3:07 PM

99Sierra2500 said:
I would look at the diagnostic section of the shop manual here: https://lemon-manuals.la/Chevrolet/2004/

Ok thanks

99Sierra2500 · Monday at 3:21 PM

I mean first. Welcome to the site though.

ORVietVet · Monday at 6:59 PM

Welcome to the forum, from Oregon.

Follow the diagnostic procedures that @99Sierra2500 recommended.

Steadicam305 · Monday at 7:05 PM

In that Lemon Manual website... Where would the reduced engine power fall under??

99Sierra2500 · Monday at 7:11 PM

Steadicam305 said:
In that Lemon Manual website... Where would the reduced engine power fall under??

Are you able to pull any codes at all?

Steadicam305 · Monday at 7:14 PM

99Sierra2500 said:
Are you able to pull any codes at all?

P1516

Throttle actuator control (tac)
module throttle actuator
position performance.

Is this the throttle body having issues??

99Sierra2500 · Monday at 7:20 PM

It's your pedal or a connection at your throttle body:

[H1]Important Information[/H1]

Subject: SES Light And Reduced Engine Power DTC P0120 P0220 P1516 P2135 - keywords accelerator actuator APP blade body connector connection DTC L33 L59 LH6 LR4 LM7 LS1 LS2 LQ4 LQ9 module position reduce sensor #PIP3089B - (10/31/2006)

Models:

2004-2006 Buick Rainer

2005-2006 Cadillac CTS-V

2003-2006 Cadillac Escalade

2003-2006 Chevrolet Avalanche, Corvette, Express, Monte Carlo, Silverado, SSR, Suburban, Tahoe, Trailblazer

2003-2006 GMC Envoy, Savana, Sierra, Yukon

2003-2006 Hummer H2

2005-2006 Pontiac GTO

Equipped with a 4.8 5.3 6.0 or 7.0 V-8 Engine

--------------------------------------------------------------------------------

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:

A vehicle may be brought into the dealer for a reduced power message, and DTCs P0120, P0220, P1516, P2101, or P2135.

The Throttle Actuator Control (TAC) / throttle body type trouble codes, may be caused by a loose wiring crimp at the throttle body connector, or a broken throttle body circuit.

Recommendation/Instructions:

Complete the current SI diagnostics for any symptoms or trouble codes found. If a intermittent T/P or TAC module type code is occurring complete the inspections below.

1. Inspect all related throttle body terminals for a loose wiring crimp. The loose crimp may be difficult to find, and the poor connection will be between the terminal and the copper strands of the wire. Wiggle test the individual throttle body circuits to see if the concern can be duplicated.

2. Inspect the related circuits for broken wires inside the insulation. The outer wire insulation may look fine, but the internal copper strands may be partially broken. Breaks in the wires usually occur within 1 to 4 inches of the throttle body connector. Wiggle testing may also induce a trouble code to set.

3. On C/K trucks complete SI procedures for voltage drop on grounds G103 and G104. Grounds G103 or G104 may be loose or corroded.

If a terminal crimp or a broken wire has been found, repair or replace only the circuits involved. There is a throttle body pigtail connector available through GMSPO, but installing this pigtail connector may cause other intermittent TAC module/TP codes at a later date. If this pigtail must be used, please follow the SI procedures for Splicing Copper Wire Using Splice Sleeves. (the proper Kent-Moore crimping tool must be used for this repair)

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

Steadicam305 · Monday at 7:21 PM

99Sierra2500 said:
It's your pedal or a connection at your throttle body:

[H1]Important Information[/H1]

Subject: SES Light And Reduced Engine Power DTC P0120 P0220 P1516 P2135 - keywords accelerator actuator APP blade body connector connection DTC L33 L59 LH6 LR4 LM7 LS1 LS2 LQ4 LQ9 module position reduce sensor #PIP3089B - (10/31/2006)

Models:

2004-2006 Buick Rainer

2005-2006 Cadillac CTS-V

2003-2006 Cadillac Escalade

2003-2006 Chevrolet Avalanche, Corvette, Express, Monte Carlo, Silverado, SSR, Suburban, Tahoe, Trailblazer

2003-2006 GMC Envoy, Savana, Sierra, Yukon

2003-2006 Hummer H2

2005-2006 Pontiac GTO

Equipped with a 4.8 5.3 6.0 or 7.0 V-8 Engine

--------------------------------------------------------------------------------

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:

A vehicle may be brought into the dealer for a reduced power message, and DTCs P0120, P0220, P1516, P2101, or P2135.

The Throttle Actuator Control (TAC) / throttle body type trouble codes, may be caused by a loose wiring crimp at the throttle body connector, or a broken throttle body circuit.

Recommendation/Instructions:

Complete the current SI diagnostics for any symptoms or trouble codes found. If a intermittent T/P or TAC module type code is occurring complete the inspections below.

1. Inspect all related throttle body terminals for a loose wiring crimp. The loose crimp may be difficult to find, and the poor connection will be between the terminal and the copper strands of the wire. Wiggle test the individual throttle body circuits to see if the concern can be duplicated.

2. Inspect the related circuits for broken wires inside the insulation. The outer wire insulation may look fine, but the internal copper strands may be partially broken. Breaks in the wires usually occur within 1 to 4 inches of the throttle body connector. Wiggle testing may also induce a trouble code to set.

3. On C/K trucks complete SI procedures for voltage drop on grounds G103 and G104. Grounds G103 or G104 may be loose or corroded.

If a terminal crimp or a broken wire has been found, repair or replace only the circuits involved. There is a throttle body pigtail connector available through GMSPO, but installing this pigtail connector may cause other intermittent TAC module/TP codes at a later date. If this pigtail must be used, please follow the SI procedures for Splicing Copper Wire Using Splice Sleeves. (the proper Kent-Moore crimping tool must be used for this repair)

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

Got it. Thanks for the info!! This has been kicking my ass lately

99Sierra2500 · Monday at 7:21 PM

[H1]Powertrain Controls Diagnosis[/H1]
DTC P1516

CIRCUIT DESCRIPTION
The predicted throttle position (TP) is compared to the actual throttle position. The two values should be within a calibrated range of each other. Both the powertrain control module (PCM) and the throttle actuator control (TAC) module redundantly monitor the predicted and actual throttle position. This DTC sets if the PCM detects an out of range condition between the predicted and the actual throttle position.

CONDITIONS FOR RUNNING THE DTC
- DTC U0107 is not set.
- The ignition switch is in the Crank or Run position.
- The ignition voltage is more than 5.23 volts.
- The TAC system is not in the battery saver mode.

CONDITIONS FOR SETTING THE DTC
- The TAC module detects that the predicted and the actual throttle positions are not within a calibrated range of each other.
- The PCM and the TAC cannot determine the throttle position.
- Both of the TP sensors are invalid.
- All of the above conditions are met for more than 1 second.

ACTION TAKEN WHEN THE DTC SETS
- The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
- The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
- The control module commands the TAC system to operate in the Reduced Engine Power mode.
- A message center or an indicator displays Reduced Engine Power.
- Under certain conditions the control module commands the engine OFF.

CONDITIONS FOR CLEARING THE MIL/DTC
- The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.

DIAGNOSTIC AIDS
- Inspect the TAC module connectors for signs of water intrusion. If water intrusion occurs, multiple DTCs may set without any circuit or component conditions found during diagnostic testing.
- Verify that the starting and charging systems are operating properly. Low system voltage can cause this DTC to set.
- When the TAC module detects a condition within the TAC system, more than one TAC system related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing an individual condition may correct more than one DTC. Disconnecting components during testing may set additional DTCs. Remember this if you review the stored information in Capture Info.
- For an intermittent, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

[H3]Steps 1-9:[/H3]

Steadicam305 · Monday at 7:22 PM

Its not a ground cable issue?

99Sierra2500 · Monday at 7:22 PM

[H3]Steps 10-18:[/H3]

The numbers below refer to the step numbers on the diagnostic table.
7. If the TP indicated angle does not follow the movement of the throttle blade and no TP sensor DTCs are set, there is a mechanical condition with the throttle shaft or the TP sensor.
18. Locating and repairing an individual condition may correct more than one DTC.

Steadicam305 · Monday at 7:23 PM

99Sierra2500 said:
[H3]Steps 10-18:[/H3]

View attachment 6199
The numbers below refer to the step numbers on the diagnostic table.
7. If the TP indicated angle does not follow the movement of the throttle blade and no TP sensor DTCs are set, there is a mechanical condition with the throttle shaft or the TP sensor.
18. Locating and repairing an individual condition may correct more than one DTC.

Got it

99Sierra2500 · Monday at 7:24 PM

Steadicam305 said:
Its not a ground cable issue?

I would check that first, it could be, it is basically carefully checking everything to trace the problem before you order any parts.

99Sierra2500 · Monday at 7:25 PM

Steadicam305 said:
Got it

I'm just taking it from the book, if it doesn't help, come back, and we can try something else.

ORVietVet · Monday at 7:35 PM

Hopefully, in the future, if there is a time when you ask for help on a problem and you know there is a CEL code........YOU SHARE THAT CODE(S)!!!

Steadicam305 · Monday at 7:41 PM

ORVietVet said:
Hopefully, in the future, if there is a time when you ask for help on a problem and you know there is a CEL code........YOU SHARE THAT CODE(S)!!!

Ok!