Sensor Power Supply High Voltage (Ford)
What does P1242 mean?
The P1242 code means the vehicle's onboard diagnostic system has detected: Sensor Power Supply High Voltage (Ford). This is a moderate severity code.
Common Symptoms
- Check Engine Light on
- Erratic sensor readings on scan tool
- Engine surging or hunting idle
- Poor fuel economy
- Hesitation during acceleration
Probable Causes (Ranked by Likelihood)
- Open ground circuit on 5-volt reference sensors Very High
- Corroded ground connection at engine block High
- Damaged wiring causing open in sensor ground Moderate
- PCM internal voltage regulator over-voltage Moderate
- Aftermarket sensor with incorrect resistance Low
Step-by-Step Diagnostic Procedure
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Check sensor ground circuits for continuity to the PCM
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Inspect engine ground straps for corrosion
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Measure 5-volt reference at the PCM output pin
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Test each sensor ground individually at the connector
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Verify correct part numbers on recently replaced sensors
Frequently Asked Questions
What causes sensor power supply to read high?
High voltage typically indicates a ground circuit problem. When a sensor loses its ground path, the signal voltage floats high because there is no return path for current.
Is P1242 a serious code?
It is moderately serious. Incorrect sensor readings can cause poor fuel economy, rough running, and potential catalytic converter damage.
Can a loose ground wire cause P1242?
Yes. A loose, corroded, or broken ground wire is one of the most common causes. Check engine-to-body ground straps and sensor ground pins at the PCM connector.