High Side Voltage Fault

The computer is seeing more voltage than it should on a specific circuit, which can cause parts to misfunction or damage. Instead of the expected 0-5 volts, it might be seeing 12-14 volts.

The engine control unit (ECU) monitors the voltage levels across various inputs. If it detects a voltage reading outside the normal range, it sets this fault code.

Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.

1. 11. Check the wiring and connectors for damage or short circuits. Look for frayed wires or corrosion at connections. Decision: If damaged, repair/replace wiring/connectors.
2. 22. Test the voltage at the sensor or actuator associated with SPN 429. Use a multimeter. Decision: If voltage is above expected range, suspect the sensor/actuator is faulty.
3. 33. If the wiring and sensor are okay, check for any recent modifications or aftermarket parts that may be affecting the voltage. Decision: If found, revert to factory specifications and test again.
4. 44. Clear the fault code and perform a road test to see if the code returns. Decision: If it returns, further diagnostics on the control circuitry may be necessary.

• Shorted wires
• Bad connectors
• Faulty sensor or actuator

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