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JKuhns
JKuhns, ASE Certified Technician
Category: Cadillac
Satisfied Customers: 152
Experience:  17+ yrs. experience, ASE Master Tech, GM STC trained
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2003 CTS Problems. Reduced engine power and service idle control

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Had problems with Reduced engine power and service idle control on my 2003 CTS. Dealer replaced the ECM and then the throttle body. Problem continues with very hard shifting. Used a piece of equipment to pull the codes and got the following in this order. . . P1776, P1795, P0700, and P2176. I have seen this issue reported by others. . . Surely someone has figured out what is causing this.

Hello,

These codes and symptoms are leaning to the throttle actuator control. This is mounted at the gas pedal. It sends signals to TCM (trans control module). This unit is critical for throttle position signals. The codes are indicating the wrong reference signal is being sent. I can see why they did throttle body as the TPS ( throttle position sensor) could do as well. But these codes are for the APP ( accelerator pedal position ) sensor.

Accelerator Pedal Position (APP) Sensor
The APP sensor is mounted on the accelerator pedal assembly. The APP is actually 2 individual APP sensors within 1 housing. These are 2 separate signal, low reference, and 5-volt reference circuits. The APP sensor 1 voltage increases as the accelerator pedal is depressed. The APP sensor 2 voltage also increases as the accelerator pedal is depressed, but the voltage range for sensor 2 is approximately half of sensor 1.

Customer: replied 7 years ago.

Hello,

I replaced the Accelerator Pedal with the sensors but that did not help. I am still getting the same codes as before. However, there is a new one that I have not seen. It is P2135. Thanks,

Hi Bob,

It sounds like you replaced most of the components involved, so it likely is a wiring problem. I have not seen a typical failure on this specific vehicle but the location, where the wiring generally breaks is where the wiring flexes when the engine moves on accel. & decel. Also check wiring under dash for chafing against a pedal or dash support. Here is the info on the code P2135: Let me know if you need more info to check the wiring.

Circuit Description

The throttle position (TP) sensors 1 and 2 are located within the throttle body assembly. The TP sensors share a common 5-volt reference circuit and a common low reference circuit. The 5-volt reference circuit is also shared with accelerator pedal position (APP) sensor 2. The 5-volt reference voltage is supplied on 2 separate engine control module (ECM) terminals, but the terminals are connected internally to the same voltage supply. Each TP sensor has an individual signal circuit, which provides the ECM with a signal voltage proportional to throttle the plate movement. When the throttle plate is in the closed position, the TP sensor 1 signal voltage is near the low reference and increases as the throttle plate is opened. The TP sensor 2 signal voltage at closed throttle is near the 5-volt reference and decreases as the throttle plate is opened. The ECM compares the signal of the throttle position sensors to the predicted TP sensor signal, based on calculations from the mass air flow (MAF) sensor. The control module also compares the signal of the TP sensor 1 and TP sensor 2 through the entire range. If the ECM detects a difference from the predicted range of more than 6 percent between sensor 1 and sensor 2, DTC P2135 sets.

Conditions for Running the DTC

The battery voltage is more than 10 volts.
The ignition is ON.

Conditions for Setting the DTC

The ECM detects that the difference between TP sensor 1 and TP sensor 2 is more than the predicted value.

Action Taken When the DTC Sets

The control module stores the DTC information into memory when the diagnostic runs and fails.
The malfunction indicator lamp (MIL) will not illuminate.
The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
The driver information center, if equipped, may display a message.

Conditions for Clearing the DTC

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 non-emission related diagnostic.
Clear the DTC with a scan tool.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Observe the DTC information with a scan tool.

Is DTC P0101, P0121, P0122, P0123, P0221, P0222, P0223, P2122, P2123, P2127, P2128 also set?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3

    1. Turn OFF the ignition.
    2. Disconnect the throttle position (TP) sensor electrical connector. Refer to Throttle Body Assembly Replacement.
    3. Disconnect the engine control module (ECM). Refer to Engine Control Module Replacement.
    4. Measure the resistance of the following circuits with a DMM for each of the TP sensors:
The low reference circuit
The TP sensor signal circuit
The 5-volt reference circuit

Is the resistance more than the specified value for any circuit?

5 ?

Go to Step 7

Go to Step 4

4

Test the signal circuit of the TP sensor 1 for a short to the signal circuit of TP sensor 2. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 9

Go to Step 5

5

Test for an intermittent and for a poor connection at the TP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 9

Go to Step 6

6

Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 9

Go to Step 8

7

Repair the high resistance in the circuit that measured above the specified value. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 9

--

8

Replace the throttle body assembly. Refer to Throttle Body Assembly Replacement.

Did you complete the replacement?

--

Go to Step 9

--

9

  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 10

10

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK

Customer: replied 7 years ago.

The Throttle Position Sensor has not been replaced. The dealer did not replace that when they replaced the Throttle Body. That was my next step. Apparently, it just bolts onto the Throttle Body. TH297 is the part number I plan to purchase.

OK, I have never seen a electronic throttle body that came without throttle position sensor. Our GM parts catalog list it all as one unit. Did they possibly get an aftermarket part? Let me know how it works out.
JKuhns, ASE Certified Technician
Category: Cadillac
Satisfied Customers: 152
Experience: 17+ yrs. experience, ASE Master Tech, GM STC trained
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