P159F
DTC P159F or P15A0
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 Descriptors
DTC P159F
-
Fuel Economy Mode Switch Circuit Low Voltage
DTC P15A0
-
Fuel Economy Mode Switch Circuit High Voltage
Diagnostic Fault Information
Circuit Description
The ECM supplies 5 V reference voltage, through the 5 V reference voltage circuit, to the 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) 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 must be pressed for between 0.094-1.5 s to activate the fuel economy mode. Voltage on the signal wire is normally between 1.45-3.45 V with the switch depressed. When the switch is released, voltage on the signal wire is normally between 3.65-4.45 V.
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 [1][2]Electrical Diagrams
Connector End View Reference
Component Connector End Views Sunshade - Left Front
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. Ignition ON, observe the scan tool Fuel Economy Mode parameter. The parameter should display Inactive.
2. Ignition ON, command the Fuel Economy ON and OFF with a scan tool. The Fuel Economy Mode parameter should display Active and Inactive as commanded.
3. 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 X1 harness connector at the Fuel Economy Mode switch.
2. Test for less than 5 ohms between the ground circuit terminal 1 of the harness connector and ground.
• If greater than the specified range, test the ground circuit for a open/high resistance and repair as necessary.
3. Ignition ON, test for 4.8-5.2 V between the 5 V reference circuit terminal 3 of the harness connector and ground.
• 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.
• 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.
4. Observe the scan tool Fuel Economy Mode Switch parameter. The parameter should display Circuit Low Voltage.
• If the parameter does not display the specified value, test the signal circuit for a short to voltage. If the circuit tests normal, replace the K20 ECM.
5. Connect a 3 A fused jumper wire between 5 V reference circuit terminal 3 of the harness connector and signal circuit terminal 4 of the harness connector. Verify the scan tool Fuel Economy Mode Switch parameter displays Circuit High Voltage.
6. If all scan tool parameter displays are normal, test or replace the S87 fuel economy mode switch.
Component Testing
1. Disconnect the fuel economy mode switch and measure between the 5 V reference voltage circuit terminal 3 of the switch and signal circuit terminal 4 of the switch for 266-294 ohms with a DMM.
• If the DMM does not measure between 266-294 ohms, replace the S87 fuel economy mode switch.
2. Measure between the 5 V reference voltage circuit terminal 3 of the switch and the ground circuit terminal 1 of the switch for 1,414-1,562 ohms with a DMM.
• If the DMM does not measure between 1,414-1,562 ohms, replace the S87 fuel economy mode switch.
3. With the fuel economy mode switch button depressed, measure between the 5 V reference voltage circuit terminal 3 of the switch and the ground circuit terminal 1 of the switch for 486ohms538 ohms with a DMM.
• If the DMM does not measure between 486-538 ohms, replace the S87 fuel economy mode switch.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* Fuel Economy Indicator Switch Replacement Service and Repair
* Control Module References Programming and Relearning for ECM replacement, setup and programming