GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 GMC T-Series Medium Duty Truck F6/F7/F8 🢒 DTC 🢒 DTC P1277

Circuit Description

The accelerator pedal position (APP) sensor is mounted on the accelerator pedal control assembly. The sensor is made up of three individual sensors within one housing. The engine control module (ECM) uses the APP sensors to determine the amount of acceleration or deceleration desired by the person driving the vehicle via the fuel injector control. The APP sensor 1 has the following circuits.

    • A 5-volt reference circuit
    • A low reference circuit
    • APP sensor 1 signal circuit

The ECM supplies 5 volts to the APP sensor 1 on the 5-volt reference circuit. The ECM also provides a ground on the low reference circuit. The APP sensor 1 provides a signal to the ECM on the APP sensor 1 signal circuit which is relative to the position changes of the accelerator pedal angle. The ECM monitors the APP sensor 1 signals for voltage outside the normal range of the APP sensor 1. If the ECM detects an excessively low APP sensor 1 signal voltage, this DTC will set.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1277 Accelerator Pedal Position (APP) Sensor 1 Circuit Low Voltage

Conditions for Running the DTC

The ignition switch is ON.

Conditions for Setting the DTC

The APP sensor 1 voltage is less than 0.25 volts.

Action Taken When the DTC Sets
    • The ECM does not illuminate the malfunction indicator lamp (MIL) when the diagnostic runs and fail.
    • The ECM records the operating conditions at the time the diagnostic fails. The ECM stores this information in the Failure Records.

Conditions for Clearing the DTC
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • Clear the DTC with a scan tool.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Turn OFF the ignition for 30 seconds.
  2. Start the engine.
  3. Observe the DTC Information with a scan tool.

Is DTC P0641 also set?

--

Go to DTC P0641

Go to Step 3

3
  1. Turn ON the ignition, with the engine OFF.
  2. Observe the Accelerator Pedal Position (APP) Sensor 1 parameter with a scan tool.

Is the APP sensor 1 parameter less than the specified value?

0.25 V

Go to Step 5

Go to Step 4

4

  1. Observe the Failure Records data for this DTC.
  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 Failure Records.

Did the DTC fail this ignition?

--

Go to Step 5

Go to Intermittent Conditions

5
  1. Turn OFF the ignition.
  2. Disconnect the APP sensor connector.
  3. Connect a DMM between the 5-volt reference circuit and low reference circuit of the APP sensor 1.
  4. Turn ON the ignition, with the engine OFF.

Is the DMM voltage more than the specified value?

5.5 V

Go to Step 6

Go to Step 7

6
  1. Turn OFF the ignition.
  2. Disconnect the APP sensor connector.
  3. Connect a 3-amp fused jumper wire between the 5-volt reference circuit and the signal circuit of the APP sensor 1.
  4. Turn ON the ignition, with the engine OFF.
  5. Observe the APP Sensor 1 parameter with a scan tool.

Is the APP Sensor 1 parameter more than the specified value?

5.5 V

Go to Step 9

Go to Step 8

7
  1. Test the 5-volt reference circuit between the engine control module (ECM) and the APP sensor 1 for the following conditions:
    2. • A short to ground
    • A short to low reference circuit
    • An open circuit
  2. Repair the circuits as necessary.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

8
  1. Test the signal circuit between the ECM and the APP sensor 1 for the following conditions:
    2. • A short to ground
    • A short to low reference circuit
    • An open circuit
  2. Repair the circuits as necessary.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

9
  1. Turn OFF the ignition.
  2. Disconnect the APP sensor connector.
  3. Inspect for poor connections at the harness connector of the APP sensor.
  4. Repair the connections as necessary.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 11

10
  1. Turn OFF the ignition.
  2. Disconnect the ECM.
  3. Inspect for poor connections at the harness connector of the ECM.
  4. Repair the connections as necessary.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

11

Replace the APP sensor. Refer to Accelerator Pedal Position Sensor Replacement .

Did you complete the replacement?

--

Go to Step 13

--

12

Important: The replacement ECM must be programmed.

Replace the ECM. Refer to Engine Control Module Replacement/Restore Fuel Rate Data , and Fuel Injector Flow Rate Programming .

Did you complete the replacement?

--

Go to Step 13

--

13
  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 3

Go to Step 14

14

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK