Upshift Switch Circuit
P0815 indicates a problem with the upshift switch circuit, typically found in vehicles with manual shift modes or paddle shifters. The PCM has detected an electrical fault such as an open circuit, short circuit, or defective switch that prevents proper upshift command recognition.
What You Might Notice
- Manual paddle upshift function disabled or non-responsive
- Shift indicator displays incorrect gear information
- Inability to manually shift to higher gears
- Check Engine light illuminated
- Transmission remains in lower gear despite upshift attempts
Most Common Causes
- 1
Defective Upshift Switch
The upshift switch (paddle or lever) has failed electrically and no longer sends proper signals to the PCM. This is the most common cause of this code.
- 2
Open Circuit in Upshift Switch Wiring
A break or loose connection in the wiring harness between the upshift switch and PCM prevents signal transmission. Check connectors and wire routing for damage.
- 3
Shorted Upshift Switch Circuit
A short circuit in the switch wiring or at the switch connector is causing incorrect voltage readings at the PCM input. This can result from damaged insulation or moisture intrusion.
- 4
PCM Programming Error or Failure
The PCM itself may have a software glitch or hardware failure preventing it from recognizing valid upshift signals. This is less common but possible on some vehicles.
How to Diagnose It
- 1
Check Defective Upshift Switch — The upshift switch (paddle or lever) has failed electrically and no longer sends proper signals to the PCM. This is the most common cause of this code.
- 2
Check Open Circuit in Upshift Switch Wiring — A break or loose connection in the wiring harness between the upshift switch and PCM prevents signal transmission. Check connectors and wire routing for damage.
- 3
Check Shorted Upshift Switch Circuit — A short circuit in the switch wiring or at the switch connector is causing incorrect voltage readings at the PCM input. This can result from damaged insulation or moisture intrusion.
- 4
Check PCM Programming Error or Failure — The PCM itself may have a software glitch or hardware failure preventing it from recognizing valid upshift signals. This is less common but possible on some vehicles.
How to Fix It
- 1
Test Upshift Switch Continuity
Use a digital multimeter to test the upshift switch for proper continuity and resistance values when activated. Compare results to manufacturer specifications. Replace the switch if out of spec.
- 2
Inspect Wiring and Connectors
Visually inspect all wiring between the upshift switch and PCM for damage, corrosion, or loose connections. Repair or reconnect as needed and test for proper voltage signals.
- 3
Replace Upshift Switch
If testing confirms the switch is defective, remove and replace it with a new OEM or quality aftermarket upshift switch. Reconnect all wiring and retest system function.
- 4
PCM Reprogramming or Replacement
If switch and wiring test good, the PCM may require reprogramming or replacement. Contact a dealership or qualified technician with PCM programming capabilities to address this.
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