P1221

CIRCUIT DESCRIPTION
The Throttle Position (TP) sensor is mounted on the throttle body assembly. The sensor is actually 2 individual TP sensors within 1 housing. Two separate signals, low reference circuits, and 5-volt reference circuits are used to connect the TP sensor assembly to the Throttle Actuator Control (TAC) module. The 2 sensors have opposite functionality. The TP sensor 1 signal voltage is pulled up to reference voltage as the throttle opens, from below 1 volt at closed throttle to above 3.5 volts at Wide Open Throttle (WOT). The TP sensor 2 signal voltage is pulled down to low reference from around 3.8 volts at closed throttle to below 1 volt at WOT. TP sensor 1 and APP sensor 1 share a 5-volt reference circuit that is connected within the TAG module. TP sensor 2 and APP sensor 2 share a 5-volt reference circuit that is connected within the TAC module. If an out-of-range condition is detected with the TP sensor 2, this Diagnostic Trouble Code (DTC) will set and the Reduced Engine Power message wilt be displayed.

TP Sensor Position Table:

The table shows the percentage and voltage readings of the scan tool based on the position of the TP.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P1517 and P1518 are not set.
^ The ignition switch is in the crank or run position.
^ The ignition voltage is more than 5.23 volts.

CONDITIONS FOR SETTING THE DTC
^ TP sensor 2 disagrees with TP sensor 1 by more than 7.5 percent.
^ All above conditions exist for less than 1 second.

ACTION TAKEN WHEN THE DTC SETS
^ The control module illuminates the Malfunction Indicator Lamp (MIL) when the diagnostic runs and fails.
^ The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame and/or the Failure Records.
^ The control module commands the TAC system to operate in the Reduced Engine Power mode.

OR

^ Under certain conditions the control module commands the engine OFF.
^ The message center displays Reduced Engine Power.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the Malfunction Indicator Lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
^ 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 emission related diagnostic.
^ Use a scan tool in order to clear the MIL and the DTC.

DIAGNOSTIC AIDS
^ Inspect the TAC module connectors for signs of water intrusion. When this occurs, multiple DTCs could be set without circuit or component conditions found during diagnostic testing.
^ When the TAC module detects a condition within the TAC system, more than 1 TAC system-related DTC may set. This condition is due to the many redundant tests that continuously run on this system. Locating and repairing 1 individual condition may correct more than 1 DTC. Disconnecting components during testing may set additional DTCs. Be aware of this condition if you review the stored information in Capture Info.
^ If this DTC is determined to be intermittent, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION

Steps 1-10:

Steps 11-21:

The number below refers to the step number on the diagnostic table.
21. 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 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. Be aware of this condition if you review the stored information in Capture Info.