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Tech Tip: Reduced Engine Power Message Displayed on GM Vehicles

Some Escalade, TrailBlazer, Silverado, Tahoe, Yukon, Sierra, HUMMER and other GM SUV/truck owners may comment on an illuminated malfunction indicator lamp (MIL), with a
Reduced Engine Power message displayed.

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Some customers may comment on an illuminated malfunction indicator lamp (MIL), with a
Reduced Engine Power message displayed.

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The technician may observe on a scan tool DTC P2135: Throttle Position (TP) Sensor 1-2 Correlation set as Current or in History.

This condition may be caused by the difference between TP Sensor 1 and TP Sensor 2 exceeding a calibrated value for more than two seconds.

Models:
2008-’11 Cadillac Escalade, Escalade ESV, Escalade EXT
2009-’11 Cadillac Escalade Two-Mode Hybrid
2008-’09 Chevrolet TrailBlazer
2008-’11 Chevrolet Avalanche, Colorado, Express, Silverado, Suburban, Tahoe
2008-’11 Chevrolet Tahoe Two-Mode Hybrid
2009-’11 Chevrolet Silverado Two-Mode Hybrid
2008-’09 GMC Envoy
2008-’11 GMC Canyon, Savana, Sierra, Sierra Denali, Yukon, Yukon Denali, Yukon XL, Yukon XL Denali
2008-’11 GMC Yukon Two-Mode Hybrid
2009-’11 GMC Sierra Two-Mode Hybrid
2008-’09 HUMMER H2
2008-’10 HUMMER H3

Equipped with Engine RPO LFA, LY2, L20, LMG, LC9, LH6, LMF, LH8, LH9, L76, LS2, LY5, LY6, L92, L96, LZ1, L94 or L9H

figure 1Attention: If a vehicle is encountered with this condition, do not replace the throttle body. Instead follow this procedure below.

Model year 2008-’10 vehicles must have the engine control module (ECM) reprogrammed with the latest software calibration as indicated in Step 35 of the procedure after the installation of the throttle position sensor cover.

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Model year 2011 vehicles do not need to have the ECM reprogrammed.

Service Procedure
Caution: Handle the electronic throttle control components carefully.

Use cleanliness in order to prevent damage.

Do not drop the electronic throttle control components. Do not roughly handle the electronic throttle control components.

Do not immerse the electronic throttle control components in cleaning solvents of any type.

figure 2Warning: Approved safety glasses and gloves should be worn when performing this procedure to reduce the chance of personal injury.
1. With a scan tool, verify that DTC P2135 is set as Current or in History.
• If DTC P2135 is set as Current or in History, proceed to step 2.
• If DTC P2135 is not set as Current or in History, refer to DTC List – Vehicle or Symptoms – Engine Controls in SI.

2. Turn off the ignition.

3. Open the hood.
Important: If at any time during this procedure the throttle body is dropped, abort this procedure and replace it with a new throttle body assembly.

figure 34. Remove the throttle body and discard the throttle body gasket.

5. Remove any loose debris and dirt from the throttle body assembly and the TP sensor cover. Inspect the throttle body for damage.

Caution: Do not use any solvent that contains Methyl Ethyl Ketone (MEK). This solvent may damage fuel system components.

6. Clean the throttle body bore and the throttle plate using a clean shop towel with GM Top Engine Cleaner, P/N 1052626, or ACDelco Upper Engine and Fuel Injector Cleaner, P/N X66-P, or an equivalent product.

Notice: Do not mount the throttle body in a vise. The throttle body can be set on the top of a soft, protected workbench area. figure 4

7. Hold the throttle body with your hand, so that the throttle position (TP) sensor cover is facing upward as shown in Figure 1.

8. Secure a rubber band around the throttle body and TP sensor cover as shown in Figure 1.

9. Turn over the throttle body and use a flathead screwdriver to remove the two clips (1, 2) as shown in Figure 2.

Discard the clips.

Notice: Do not pry on the machined sealing surface of the throttle body inlet duct.

figure 510. Turn over the throttle body and use a flathead screwdriver to remove the four remaining clips from the TP sensor cover.

Discard the clips.

11. Hold the throttle body with your hand, so that the TP sensor cover is facing upward.

Grasp the TP sensor cover and carefully lift it up and separate it from the throttle body.

Notice: Do not allow the intermediate gear to fall out. See Figure 3.

12. Maintain the throttle body in an upward position. Use your thumb to maintain contact with the intermediate gear.

– If the intermediate gear falls out and impacts a hard workbench surface or the floor, abort this procedure and replace with a new throttle body assembly. figure 6

13. Verify that the TP sensor cover gasket has remained in the TP sensor cover. Ensure that the gasket is accounted for and remains with the old TP sensor cover.

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14. Observe the TP sensor cover for missing female throttle actuator motor terminals (Figure 4).

Verify that the female throttle actuator motor terminals have remained in the TP sensor cover and have not been retained on the throttle actuator motor male terminals (Figure 5, 2).

Discard the old TP sensor cover, gasket and terminals.

• If one or both of the TP sensor cover female throttle actuator motor terminals have been retained on the throttle actuator motor male terminals (2), remove and discard those female terminals.

15. Remove the new TP sensor cover from the protective shipping wrapper.

16. Place the TP sensor cover in the position as shown in Figure 6. Confirm the TP sensor drive slot orientation is aligned in the TP sensor cover as shown. figure 7

If the TP sensor drive slot orientation is not aligned, use a small flathead screwdriver to ­gently rotate the TP sensor drive slot clockwise to the wide open throttle (WOT) position.

17. Verify that the TP sensor cover gasket is secure and properly positioned.

Notice: The three TP sensor cover alignment tabs are highlighted in white for identification purposes only.

18. Verify that all three of the TP sensor cover alignment tabs are present and are not damaged.

19. Grasp and hold the throttle body in the previously hand-held upward position.

Lightly depress the intermediate gear to verify that it is fully seated and the gears are engaged.

20. Rotate the throttle body plate to the WOT position.

Figure 821. Position and install the TP sensor cover to the throttle body. Hold the TP sensor cover in position. If necessary for ease of the clip installation, secure a rubber band around the throttle body and TP sensor cover.

22. Install the first TP sensor cover clip (1) in the position shown in Figure 7.

23. Install the remaining TP sensor cover clips in the sequence shown in Figure 8.

24. Install a new throttle body gasket to the intake manifold.

25. Install the throttle body, bolts and nuts. Do not tighten the fasteners yet.

26. Connect the electrical connector to the throttle body.

27. Turn on the ignition. Clear the DTC with a scan tool.

28. Observe the scan tool TP Sensor 1 and 2 Agree/Disagree parameter while slowly ­depressing the accelerator pedal to WOT and then slowly returning the pedal to closed throttle.

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Repeat the procedure several times.

Rapidly depress the accelerator pedal from the rest position to the WOT position and release the pedal. Repeat the procedure several times.

The TP Sensor 1 and 2 Agree/Disagree parameter should display Agree.

• If it displays Agree, proceed to Step 29.

• If it displays Disagree, replace the throttle body assembly.

29. Observe the ECM module DTC information. Are DTC P1516, P2101 and/or P2176 set?

• If DTC P1516, P2101 and/or P2176 are set, replace the throttle body.

• If DTC P1516, P2101 and/or P2176 are not set, proceed to Step 30.

30. Tighten the throttle body fasteners to 10 Nm (89 lb.-in.).

31. Install any remaining components that were removed during this procedure.

32. Verify the battery voltage is more than 12 volts but less than 16 volts before proceeding with ECM reprogramming.

33. During reprogramming, the battery voltage must be maintained within the proper range of 12-15 volts. Connect the approved Midtronics PSC 550 Battery Maintainer (SPS Programming Support Tool EL-49642) to the vehicle.

• If the above recommended tool is not available, do not connect a battery charger to the vehicle. Connect a fully charged 12V jumper or booster pack that is disconnected from the AC voltage supply.

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34. Use a Tech 2 or a multiple diagnostic interface (MDI) module for reprogramming. Ensure that either device is updated with the latest available software version before performing the reprogramming event.

35. Reprogram the ECM using the Service Programming System (SPS) with the latest calibration available on TIS2WEB. Refer to the SPS procedures in SI.

36. Perform the Throttle Learn Reset Procedure. Refer to Throttle/Idle Learn > Throttle Learn > Reset Procedure in SI.

Courtesy of Mitchell 1.

 

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