Applicable Systems
OBD-II
Symptoms
TPS signal voltage above maximum; ECM sees wide open throttle at all times; may run very rich.
Possible Causes
- TPS signal wire short to +5V or +12V
- TPS internal failure
- TPS ground circuit open
Troubleshooting Steps
- Step 1: Check TPS signal wire for short to +V
No short to +V - Step 2: Check TPS ground circuit continuity
Ground < 1 ohm - Step 3: Replace TPS if signal still high
New TPS signal normal - Step 4: Clear code and verify throttle operation
Throttle responds correctly - Step 5: Check for ECM +5V supply overload
+5V supply stable
How to Reset
Clear with OBD-II scanner after repair.
Common Replacement Parts
- Throttle Position Sensor (OEM spec)
Frequently Asked Questions
- Q: Why does P0123 cause rich running?
ECM sees WOT signal and enriches mixture for maximum power. This causes poor fuel economy, rough idle, and potential spark plug fouling.
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Source: SAE J2012 standard DTC list + OBD-II portal
Category: OBD-II
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