The auxiliary transmission fluid pump (ATFP) system supplies the transmission with hydraulic pressure when the vehicle is operating in the internal combustion engine (ICE) Autostop hybrid mode. The ATFP system consists of an ATFP control module that operates an electric, 12V 3 phase alternating current (ac), motor-driven pump. Two pulse width modulated (PWM) status circuits connect the ATFP control module to the hybrid powertrain control module (HPCM). The transmission auxiliary oil pump control circuit delivers the HPCM commanded pump speed to the ATFP control module. The transmission auxiliary oil pump diagnostic circuit supplies the HPCM with the actual pump speed and also with the operating status of the ATFP control module. The HPCM monitors these circuits for fault conditions.

The ATFP control module inverts 12V direct current (dc) into 12V, 3 phase ac current to operate the pump motor.

The ATFP control module monitors the status of the ATFP motor/pump as well as its own internal circuitry. The ATFP control module does not store its own diagnostic status. Current ignition cycle diagnostic status is reported to the HPCM over the transmission auxiliary oil pump diagnostic circuit. The diagnostic status within the ATFP control module is reset at every ignition-off cycle.

The HPCM observes the difference between actual and commanded ATFP pump speed is greater than 500 RPM for 4 out of 4.125 seconds.

DTC P2797 is a Type B DTC.

Schematic Reference

Hybrid Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Special Tools

J 38522 Variable Signal Generator

1. Ignition ON with the engine OFF, command the Aux. Trans. Pump Speed to 50 percent with the scan tool. Attempt to maintain pump operation for at lease 60 seconds.
2. Observe the aux. trans. fluid pump actual display and the aux. trans. fluid pump commanded displays with the scan tool. Actual pump speed should be maintained within 10 percent of commanded. The pump should not make excessive noise ro stall.

⇒	If the actual speed is within 10 percent of commanded speed an electrical fault condition is not currently present, if an aux. trans. fluid pump pressure fault is suspected, test the aux. trans. pump line pressure output. Refer to Line Pressure Check.

⇒	If the difference between actual and commanded speed is greater than 10 percent, the pump is noisy, or the pump stalls, proceed to Circuit/System Testing.

1. Inspect for DTC P0C2B. Diagnose P0C2B before performing this procedure.
2. Ignition ON, engine OFF, observe the Aux. Trans. Fluid Pump Fault Status 1 and Aux. Trans. Fluid Fault Status 2 displays with the scan tool.
3. Command the aux. trans. fluid pump speed to 50 percent with the scan tool while observing the fault status displays.

⇒	Refer to the applicable diagnostic procedure below for the fault status indicated by the scan tool display.

⇒	If No Fault status is displayed, review the Freeze Frame/Failure Records and perform the diagnosis indicated by the Fault Status parameter display.

PWM Input Fault

1. Ignition OFF, disconnect PIM connector X1.
2. Ignition ON, test for 11-13V on the Trans. Aux. Oil Pump Control circuit from PIM connector X1 terminal 5 and chassis ground.

⇒	If less than the specified range, test the control circuit for an open or short to ground. If the circuit tests normal, replace the ATFP Control Module.

Important: Only connect the J 38522 to the ATFP control circuit when adjusted to 50 percent duty cycle. Duty cycles of less than 50 percent may damage the ATFP pump assembly.

3. Pre-Adjust the J 38522 variable signal generator to 50 percent duty cycle @ 250 Hz.
4. Connect the J 38522 variable signal generator to the Trans. Aux. Oil Pump Control circuit, from the PIM connector X1 terminal 5 and ground and listen for ATFP motor operation.

⇒	If pump operation is audible, replace the PIM.

⇒	If pump operation is not audible, continue with Circuit/System Testing.

5. Ignition OFF, disconnect the ATFP control module connector X1.
6. Ignition ON, test for 0V on the Trans. Aux. Oil Pump control circuit from PIM connector X1 terminal 5 and chassis ground.

⇒	If greater than the specified range, test the control circuit for a short to voltage.

⇒	If equal to the specified range, replace the ATFP control module.

Motor/Open Short

This display indicates the ATFP control module has detected one of the following pump motor current conditions:

1. Ignition OFF, disconnect the ATFP control module connector X2.
2. Using the Auxiliary Fluid Pump Specification table listed below, test the resistance between the X2 circuits of the pump connector as indicated.

⇒	If any of the circuits are not within the specified range, replace the pump assembly and repeat the Circuit/System Verification.

⇒	If all circuits test normal, replace the ATFP control module and repeat Circuit/System Verification.

Motor CKT Fault

This display indicates an internal ATFP control module fault exists, no external circuits are involved. Replace the ATFP control module.

Temp Sen Fault

This display indicates an internal ATFP control module fault exists, no external circuits are involved. Replace the ATFP control module.

Low Voltage

1. This display indicates the ATFP control module has monitored battery voltage of less than 12.6V.
2. Measure actual battery voltage with a DMM.

⇒	If actual battery voltage measures less than the value range, increase actual battery voltage and repeat Circuit/System Testing.

⇒	If actual battery voltage measures more than the value range, test the ATFP control module power and ground circuits for a high resistance condition. If the circuits test normal, replace the ATFP control module.

ATFPCM Over temp

1. This display indicates the ATFP control module circuit board has reached a temperature of 115-125°C (239-257°F).
2. Measure the actual temperature of the ATFP control module case.

⇒	If actual temperature is the same or more than the value range, no action is necessary.

⇒	If actual temperature is less than the value range, replace the ATFP control module.

ATFPCM Hot

1. This display indicates the ATFP control module circuit board has reached a temperature of more than 125°C (257°F).
2. Measure the actual temperature of the ATFP control module case.

⇒	If actual temperature is the same or more than the value range, no action is necessary.

⇒	If actual temperature is less than the value range, replace the ATFP control module.

Current High/Lo

1. This display indicates the ATFP control module has monitored motor current that is outside the normal range for a given motor speed.
2. Inspect for the following conditions:

•	Low or cavitating automatic transmission fluid

•	Poor terminal connection or wiring degradation

•	External indication of ATFP pump motor damage

⇒	If none of the conditions are observed, replace the ATFP motor/pump assembly and the ATFP control module.

Current Fault

This display indicates an internal ATFP control module fault exists, no external circuits are involved. Replace the ATFP control module.

Unable to Start

1. This display indicates the ATFP control module has monitored motor current of more than 20 A during motor start-up.
2. Inspect for the following conditions:

•	Automatic transmission fluid pressure trapped internally

•	Poor terminal connection or wiring degradation

•	External indication of ATFP pump motor damage

⇒	If none of the conditions are observed, replace the ATFP motor/pump assembly and the ATFP control module.

No PWM Response

This display indicates the HPCM does not detect the ATFP Control Feedback circuit signal. Refer to DTC P0C2B.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.