Throttle Position Sensor Reference Voltage Low (GM)
What does P1219 mean?
The P1219 code means the vehicle's onboard diagnostic system has detected: Throttle Position Sensor Reference Voltage Low (GM). This is a moderate severity code.
Common Symptoms
- Check Engine Light on
- Reduced engine power message
- Erratic idle speed
- Poor throttle response
- Possible limp mode
Probable Causes (Ranked by Likelihood)
- Faulty TPS or throttle body assembly Very High
- Low 5V reference voltage from PCM High
- Short to ground in 5V reference wire Moderate
- Another sensor on the 5V reference circuit pulling voltage down Moderate
- PCM internal 5V reference fault Low
Step-by-Step Diagnostic Procedure
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Measure the 5V reference voltage at the TPS connector with key on engine off
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If below 4.5V, disconnect other sensors on the same 5V reference circuit one at a time
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When the voltage returns to 5V after disconnecting a sensor, that sensor is shorted
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Inspect TPS connector and wiring for shorts to ground
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Replace the faulty sensor or repair the wiring
Frequently Asked Questions
What is the 5V reference circuit?
The PCM supplies a 5V reference voltage to multiple sensors including the TPS, MAP sensor, and accelerator pedal position sensor. If this reference voltage drops, all sensors on that circuit can give false readings.
Why do I need to disconnect sensors one at a time?
Multiple sensors share the same 5V reference. If one sensor shorts internally and pulls the voltage down, all other sensors on that circuit are also affected. Disconnecting them one at a time identifies the culprit.
Can P1219 cause the reduced engine power warning?
Yes. Low TPS reference voltage causes the PCM to read incorrect throttle position. As a safety measure, the PCM activates Reduced Engine Power mode to prevent unintended acceleration.