P2121

DTC P2121

CIRCUIT DESCRIPTION
The accelerator pedal position (APP) sensor is mounted on the accelerator pedal assembly. The sensor is actually 3 individual APP sensors within 1 housing. Three separate signal, low reference and 5-volt reference circuits connect the APP sensor assembly to the throttle actuator control (TAC) module.

Each sensor has a unique functionality. The APP sensor 1 signal is pulled up to the reference voltage as the accelerator pedal is depressed, from below 1 volt at 0 percent pedal travel, with the pedal at rest. To above 2 volts at 100 percent pedal travel, with the pedal fully depressed. The APP sensor 2 signal is pulled down to the low reference from above 4 volts at 0 percent pedal travel to below 2.9 volts at 100 percent pedal travel. The APP sensor 3 signal is pulled down to low reference from above 3.8 volts at 0 percent pedal travel to below 3.1 volts at 100 percent pedal travel. TP sensor 1 and APP sensor 1 share a 5 volt reference circuit that is connected within the TAC module. TP sensor 2 and APP sensor 2 share a 5-volt reference circuit that is connected within the TAC module. If only 1 APP sensor DTC is set, the redundant APP systems allow the TAC system to continue operating normally. One APP sensor DTC will not cause the Reduced Engine Power message to be displayed. Two APP sensor DTCs for the same sensor also will not cause the Reduced Engine Power message to be displayed. If an out of range condition is detected with the APP sensors, DTC 2121 sets.

CONDITIONS FOR RUNNING THE DTC
- DTCs P0606, P2108, or U0107 are not set.
- The ignition switch is in the crank or run position.
- The ignition voltage is greater than 5.23 volts.

CONDITIONS FOR SETTING THE DTC
- APP sensor 1 disagrees with APP sensor 2 by more than 10.5 percent and APP sensor 1 disagrees with APP sensor 3 by more than 13 percent.
- 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.
- The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
- If one or more APP sensor DTCs are set for a single APP sensor, the following occurs:
- The control module will not command Reduced Engine Power mode.
- 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.
- The message center displays Reduced Engine Power.
- If all three APP sensors are out of range, the following occurs:
- The control module commands Reduced Engine Power mode.
- The APP indicated angle is limited to 0 percent. The control module only allows the engine to idle.
- The message center displays Reduced Engine Power.

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
- Inspect the TAC module connectors for signs of water intrusion. When water intrusion occurs, multiple DTCs could be set with no DTC circuit or component conditions found during diagnostic testing.
- When the TAC module detects throttle movement with a DTC P2120 set, a DTC P2121 also sets.
- When the TAC module detects a condition within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests that run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting components during testing may set additional DTCs. Keep this in mind when reviewing the Capture Info.
- For an intermittent, refer to Intermittent Conditions. Diagnostic Strategies

TEST DESCRIPTION

Steps 1-4:

Steps 5-7:

Steps 8-11:

Steps 12-16:

Steps 17-19:

The numbers below refer to the steps numbers in the diagnostic table.
2. This step determines if a communication condition exists.
5. This step isolates an internal APP sensor failure. The condition may only occur at a certain accelerator pedal position. Monitoring the APP angles for sensor 2 and sensor 3 is an accurate way of verifying the actual position of the pedal. The APP angles for all 3 sensors should be within a few percentages of each other. When the pedal is at rest, the APP angle for all 3 sensors should be 0 percent. When the pedal is fully depressed, all APP angles should be 100 percent.
6. The APP sensor 1 shares a common 5-volt reference circuit with the TP sensor 1. Monitoring the TP sensor 1 voltage aids in diagnosing the APP sensor 5-volt reference and the low reference circuits. If the scan tool displays near 0 volts then the circuits are OK.
9. With the TAC module still connected, this test will help determine a short to the signal circuit either within the TAC module or the wiring.
10. This step determines whether the TAC module or a shorted circuit is causing the condition.
19. When the TAC module detects a condition within the TAC system, more than 1 TAC system related DTC may set. This is due to the many redundant tests that run continuously on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting the components during testing may set additional DTCs. Keep this in mind when reviewing the Capture Info.