GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Chevy C Cab/Chassis HD (GMT 400) 🢒 Engine 🢒 Engine Controls - 6.5L (L65) 🢒 DTC P1654

Circuit Description

A dash light is illuminated by the powertrain control module (PCM) if the diagnostics has detected certain errors related to the accelerator pedal position (APP) sensor. When the PCM is commanding the Service Throttle Soon lamp ON, the voltage potential of the circuit will be low (near 0 volts). When the PCM is commanding the Service Throttle Soon Lamp OFF, the voltage potential of the circuit will be high (near battery voltage). The primary function of the PCM in this circuit is to supply the ground for the Service Throttle Soon lamp.

Conditions for Running the DTC

The ignition is in the ON position.

Conditions for Setting the DTC
    • The Service Throttle Soon lamp is requested ON.
    • The voltage on the Service Throttle Soon control circuit is high (near the battery voltage).
        or
    • The Service Throttle Soon lamp is requested OFF.
    • The voltage on the Service Throttle Soon control circuit is low (near 0 volts).

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.

Diagnostic Aids

A faulty bulb or the control circuit shorted to ground will cause a DTC P1654 to set.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. Be sure that both the ON and the OFF states are commanded. Repeat the commands as many times as necessary.

    2.

  2. If no trouble is found in the control circuit or the connections at the PCM, the PCM maybe malfunctioning, however, this is an extremely unlikely failure.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Turn ON the ignition, with the engine OFF.
  2. Using a scan tool, command the lamp ON and OFF.

Does the lamp illuminate with each command?

Go to Step 3

Go to Step 4

3

The DTC is intermittent. If no additional DTCs are stored, refer to Diagnostic Aids. If additional DTCs were stored, refer to those tables.

Are any additional DTCs stored?

Go to Diagnostic Trouble Code (DTC) List

Go to Diagnostic Aids

4
  1. Turn OFF the ignition.
  2. Disconnect the PCM connector containing the lamp control circuit.
  3. Turn ON the ignition, with the engine OFF.

Does the lamp illuminate?

Go to Step 7

Go to Step 5

5

With a fused jumper wire connected to ground, probe the lamp control circuit in the PCM harness connector.

Does the lamp illuminate?

Go to Step 6

Go to Step 8

6
  1. Check for proper connections at PCM.
  2. If a problem was found, repair as necessary.

Did you find and correct the condition?

Go to Step 10

Go to Step 9

7

Repair the short to ground in the Service Throttle Soon lamp control circuit.

Did you complete the repair?

Go to Step 10

--

8
  1. Check the Service Throttle Soon circuit for the following conditions:
    2. • Open ignition 1 voltage to the bulb
    • Malfunctioning bulb
    • Control circuit open or shorted to battery voltage
  2. Repair the problem as necessary.

Did you complete the repair?

Go to Step 10

--

9

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

Go to Step 10

--

10
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 11

Go to Step 2

11

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK