DTC P1278 Without RPO CTF
| Table 1: | APP Sensor Position Table |
| Table 2: | DTC P1278 APP sensor 1 high voltage |
Circuit Description
The accelerator pedal position (APP) sensor is mounted on the accelerator pedal control assembly. The sensor is made up of 3 individual sensors within 1 housing. Three separate signal, low reference, and 5-volt reference circuits are used in order to interface the APP sensor with the engine control module (ECM). Each sensor has a unique fuctionality to determine pedal position as shown in the table below. The ECM uses the APP sensor to determine the amount of acceleration or deceleration desired by the person driving the vehicle via fuel injector control. This DTC sets if the ECM determines an out of range condition with the APP sensor.
APP Sensor | Actual Pedal Position | % Depressed as Observed on a Scan Tool | Voltage as Observed on a Scan Tool |
|---|---|---|---|
1 | Pedal at rest | 0 | .52 - .80 |
1 | Pedal at full travel | 100 | 2.12 - 2.78 |
2 | Pedal at rest | 0 | 4.25 - 4.53 |
2 | Pedal at full travel | 100 | 2.24 - 2.93 |
3 | Pedal at rest | 0 | 3.95 - 4.13 |
3 | Pedal at full travel | 100 | 2.69 - 3.16 |
Conditions for Running the DTC
| • | DTCs P0641 or P0651 are not set. |
| • | The ignition switch is in the crank or run position. |
| • | The ignition voltage is between 7-16 volts. |
Conditions for Setting the DTC
| • | The APP sensor 1 voltage is more than 4.75 volts. |
| • | All of the above conditions are present for less than 1 second. |
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. |
| • | If one or more APP sensor DTCs are set for a single APP sensor, the control module will use the remaining two APP sensors to calculate throttle response. |
| • | If certain multiple APP sensor DTCs are set for more than one APP sensor, the following occurs: |
| - | The control module commands Reduced Engine Power mode. |
| - | The APP indicated angle is limited to a predetermined value to limit the amount of throttle control. |
| • | If all three APP sensors are out of range, the APP indicated angle is limited to 0 percent. The control module only allows the engine to idle. |
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-Engine Controls? | -- | Go to Step 2 | |
2 |
Does the DTC fail this ignition? | -- | Go to Step 4 | Go to Step 3 |
3 |
Did this DTC fail this ignition, during the above test? | -- | Go to Step 9 | Go to Intermittent Conditions |
4 |
Does the scan tool indicate the APP sensor 1 voltage at the specified value? | 0 V | Go to Step 5 | Go to Step 6 |
5 |
Does the scan tool indicate APP sensor 2 voltage at the specified value? | 0 V | Go to Step 10 | Go to Step 8 |
6 |
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 7 |
7 |
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 11 |
8 |
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 11 |
9 | Repair the intermittent condition as necessary. Refer to Connector Repairs and Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 14 | -- |
10 | Inspect for poor connections at the harness connector of the APP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 12 |
11 | Inspect for poor connections at the harness connector of the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 13 |
12 | Replace the APP sensor assembly. Did you complete the replacement? | -- | Go to Step 14 | -- |
13 | Replace the ECM. Refer to Engine Control Module Replacement/Restore Fuel Rate Data . Did you complete the replacement? | -- | Go to Step 14 | -- |
14 |
Does the DTC run and pass? | -- | Go to Step 15 | Go to Step 2 |
15 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
DTC P1278 With RPO CTF
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 high APP sensor 1 signal voltage, this DTC will set.
Conditions for Running the DTC
The ignition switch is ON.
Conditions for Setting the DTC
The APP sensor 1 voltage is more than 4.75 volts.
Action Taken When the DTC Sets
| • | The ECM does not illuminate the malfunction indicator lamp (MIL) when the diagnostic runs and tails. |
| • | 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 - Engine Controls? | -- | Go to Step 2 | |
2 |
Is the APP Sensor 1 parameter more than the specified value? | 4.75 V | Go to Step 4 | Go to Step 3 |
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions |
4 |
Is DTC P0641 also set? | -- | Go to Step 5 | Go to Step 6 |
5 |
Is the APP sensor 1 parameter less than the specified value? | 0.25 V | Go to DTC P0641 | Go to Step 8 |
6 |
Is the APP Sensor 1 parameter more than the specified value? | 4.75 V | Go to Step 8 | Go to Step 7 |
7 |
Is the DMM voltage within the specified range? | 4.5-5.5 V | Go to Step 8 | Go to Step 9 |
8 |
Important: The APP sensor 1 may be damaged if there is a circuit short to a voltage source.
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 10 |
9 |
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 11 |
10 |
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 12 |
11 |
Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 13 |
12 | Replace the APP sensor. Refer to Accelerator Pedal Position Sensor Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- |
13 |
Important: The replacement ECM must be programmed. Replace the ECM. Refer to Engine Control Module Replacement/Restore Fuel Rate Data . Did you complete the replacement? | -- | Go to Step 14 | -- |
14 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 15 |
15 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
