DTC P0121: TP SENSOR PERFORMANCE Chevrolet Chevy Express H2500

DTC P0121: TP SENSOR PERFORMANCE

Note. To locate components, see COMPONENT LOCATIONS . For circuit reference, see WIRING DIAGRAMS . For connector terminal identification, see CONNECTOR IDENTIFICATION . If an intermittent condition exists, see INTERMITTENT CONDITIONS under SELF-DIAGNOSTIC SYSTEM. If testing requires component removal or replacement, see appropriate REMOVAL & INSTALLATION article. If diagnosis requires testing of sensor operating range, see appropriate table in SENSOR OPERATING RANGE CHARTS - TRUCKS article.

The Throttle Position (TP) sensor is used by the Powertrain Control Module (PCM) to determine the throttle plate angle for various engine management systems. The TP sensor is a potentiometer type sensor with the following circuits

1. A 5-volt reference circuit.
2. A low reference circuit.
3. A signal circuit.

The PCM provides the TP sensor with a 5-volt reference circuit and a low reference circuit and a ground on the low reference circuit. Rotation of the TP sensor rotor from the closed throttle position to the Wide Open Throttle (WOT) position provides the PCM with a signal voltage from less than 1 volt to more than 4 volts through the TP sensor signal circuit. When the conditions for running this DTC are met, the PCM will use the MAP sensor in order to determine if the predicted operating range of the TP sensor is correct. If the PCM detects the TP sensor voltage is out of the predicted range, DTC P0121 sets.

1. DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0122, P0123, P0506, and P0507 are not set.
2. The engine is running for more than 2 minutes.
3. The Engine Coolant Temperature (ECT) is more than 158°F (70°C).
4. The MAP is less than 43 kPa for a TP sensor skewed high test.
5. The MAP is more than 67 kPa for a TP sensor skewed low test.
6. The MAP is steady for 2 seconds or more.
7. The TP does not vary more than 1.5 percent for 2 seconds or more.

1. The PCM detects that the TP sensor voltage is more than a predicted value when the MAP is less than 43 kPa.
2. The PCM detects that the TP sensor voltage is less than a predicted value when the MAP is more than 67 kPa.
3. The above conditions are present for 1 second.

1. The control module illuminates the Malfunction Indicator Light (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
2. The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.