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DTC P159F or P15A0

DTC P159F or P15A0

Diagnostic Instructions


• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• Diagnostic Procedure Instructions provide an overview of each diagnostic category.


DTC Descriptors

DTC P159F

Fuel Economy Mode Switch Circuit Low Voltage

DTC P15A0

Fuel Economy Mode Switch Circuit High Voltage

Diagnostic Fault Information

Circuit Short to Ground High Resistance Open Short to Voltage Signal Performance
Fuel Economy Mode Switch 5 V Reference P159F P159F, P15A1 P159F P15A0 P15A1
Fuel Economy Mode Switch Signal P159F P159F P159F P15A0 P15A1
Fuel Economy Mode Switch Ground - P15A0, P15A1 P15A0 - P15A1


Circuit Description

The ECM supplies 5 V reference voltage, through the 5 V reference voltage circuit, to the S87 fuel economy mode switch. The 5 V reference voltage causes current to flow through a series of resistors in the switch to the switch ground circuit. The ECM monitors the reference voltage through a discrete fuel economy mode switch signal circuit. When the switch button is momentarily pressed, the switch contacts allow the 5 V reference voltage to by-pass one of the resistors. The ECM detects the resulting voltage drop as a fuel economy mode request and sends a GMLAN message to the transmission control module (TCM) confirming the request. When the TCM receives the request, throttle progressions and transmission shift points are modified to optimize fuel efficiency. The instrument panel cluster (IPC) also receives the fuel economy mode request message from the ECM and illuminates the fuel economy mode indicator lamp. The fuel economy mode switch must be pressed for between 0.094-1.5 s to activate the fuel economy mode.

Conditions for Running the DTC


• Ignition key must be turned to ON.

• DTCs P159F and P15A0 run continuously when the above condition is met.


Conditions for Setting the DTC

The ECM detects that the voltage on the fuel economy mode switch signal wire is either too low or too high out of range.

Action Taken When the DTC Sets

DTCs P159F and P15A0 are Type B DTCs

Conditions for Clearing the MIL/DTC

DTCs P159F and P15A0 are Type B DTCs

Reference Information

Schematic Reference

Engine Controls Schematics (3.0L (LF1)) Engine Controls Schematics (2.8L (LAU))

Connector End View Reference

Component Connector End Views

Electrical Information Reference


• Circuit Testing

• Connector Repairs

• Testing for Intermittent Conditions and Poor Connections

• Wiring Repairs


DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification


1. Ignition ON, verify the fuel economy mode indicator lamp on the instrument panel cluster is not illuminated.

2. Ignition ON, verify the fuel economy mode indicator lamp on the instrument panel cluster illuminates when the fuel economy mode switch button is pressed.

3. Engine running, observe the scan tool DTC information. DTCs P159F and P15A0 should not set.

4. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.


Circuit/System Testing

Note

You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.



1. Ignition OFF, disconnect the harness connector at the S87 fuel economy mode switch.

2.
Note

It may take up to 2 minutes for all vehicle systems to power down.


Ignition OFF and all vehicle systems OFF, test for less than 5 Ω between ground circuit terminal 2 of the harness connector and ground.

3. If greater than the specified value, test the ground circuit for an open/high resistance and repair as necessary.

4. Ignition ON, test for 4.8-5.2 V between 5 V reference circuit terminal 9 of the harness connector and ground.

5. If less than the specified range, test the 5 V reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K20 ECM.

6. If greater than the specified range, test the 5 V reference circuit for a short to voltage. If the circuit tests normal, replace the K20 ECM.

7. Ignition ON, test for 0.060-0.250 V between signal circuit terminal 10 of the harness connector and ground.

8. If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K20 ECM.

9. If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the K20 ECM.

10. If all circuits test normal, test or replace the S87 fuel economy mode switch.


Component Testing


1. Ignition OFF, disconnect the S87 fuel economy mode switch.

2. Test for 266-294 Ω between 5 V reference voltage circuit terminal 9 and signal circuit terminal 10 of the S87 fuel economy mode switch.

3. If not within the specified range, replace the S87 fuel economy mode switch.

4. Test for 1,414-1,562 Ω between 5 V reference voltage circuit terminal 9 and ground circuit terminal 2 of the S87 fuel economy mode switch.

5. If not within the specified range, replace the S87 fuel economy mode switch.

6. With the S87 fuel economy mode switch button depressed, test for 486-538 Ω between 5 V reference voltage circuit terminal 9 and ground circuit terminal 2 of the S87 fuel economy mode switch.

7. If not within the specified range, replace the S87 fuel economy mode switch.


Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for ECM replacement, setup and programming