P15A1
DTC P15A1
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions)provide an overview of each diagnostic category.
DTC Descriptor
DTC P15A1
- Fuel Economy Mode Switch Performance
Diagnostic Fault Information
Circuit Description
The ECM supplies 5 V reference voltage, through the 5 V reference voltage circuit, to the S87 fuel economy mode switch. This 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 5 V 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 signal 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) indicating 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 button must be pressed for between 0.094-1.5 s to activate the fuel economy mode.
Conditions for Running the DTC
* The ignition key is turned to ON.
* DTC P15A1 runs 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 in an indeterminate range.
Action Taken When the DTC Sets
DTC P15A1 is a Type B DTC.
Conditions for Clearing the MIL/DTC
DTC P15A1 is a Type B DTC.
Reference Information
Schematic Reference
Engine Controls Schematics (LAU) ([1][2]Electrical Diagrams)Engine Controls Schematics (LF1) ([1][2]Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference
Control Module References (Programming and Relearning)for scan tool information
Circuit/System Verification
1. Verify that DTCs P159F and P15A0 are not set.
• If either or both of the DTCs are set, diagnose those DTCs first.
2. Ignition ON, verify the fuel economy mode indicator lamp on the instrument panel cluster is not illuminated.
3. Ignition ON, verify the fuel economy mode indicator lamp on the instrument panel cluster illuminates when the fuel economy mode switch button is pressed.
4. Engine running, observe the DTC information with a scan tool. DTC P15A1 should not set.
5. 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.
Note: It may take up to 2 minutes for all vehicle systems to power down.
2. Ignition OFF, and all vehicle systems OFF, test for less than 5 ohm between ground circuit terminal 2 of the harness connector and ground.
• If greater than the specified value, test the ground circuit for an open/high resistance and repair as necessary.
3. Test for 266-294 ohm between 5 V reference voltage circuit terminal 9 and signal circuit terminal 10 of the S87 fuel economy mode switch.
• If not the specified range, replace the S87 fuel economy mode switch.
4. Test for 1,414-1,562 ohm between 5 V reference voltage circuit terminal 9 and ground circuit terminal 2 of the S87 fuel economy mode switch.
• If not the specified range, replace the S87 fuel economy mode switch.
5. With the fuel economy mode switch button depressed, test for 486-538 ohm between 5 V reference voltage circuit terminal 9 and ground circuit terminal 2 of the S87 fuel economy mode switch.
• If not the specified range, replace the S87 fuel economy mode switch.
6. Disconnect the X2 harness connector at the ECM.
7. Test for less than 5 ohm between 5 V reference voltage circuit terminal 14 of the ECM harness connector and 5 V reference voltage circuit terminal 9 of the fuel economy mode switch harness connector.
• If greater than the specified value, repair the 5 V reference voltage circuit as necessary.
8. Test for less than 5 ohm between signal circuit terminal 29 of the ECM harness connector and signal circuit terminal 10 of the fuel economy mode switch harness connector.
• If greater than the specified value, repair the signal circuit as necessary.
9. If all circuits test normal, replace the K20 ECM.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
Control Module References (Programming and Relearning)for ECM replacement, setup and programming