Since your gauge is intermittently malfunctioning (sometimes working correctly, then spiking), the problem is *much more likely* to be with the gauge itself, the gauge wiring, or perhaps a faulty sending unit (the sensor itself might be intermittently failing) rather than its location. A consistently high reading *usually* points to a sensor problem, but the intermittent nature suggests a wiring or gauge issue.
To find the sensor:
1. Consult a repair manual: A repair manual specific to your 2004 Envoy 4.2L will have a diagram showing the exact location of the oil pressure sensor. This is the most reliable method.
2. Visual inspection: With the engine cool, locate the oil filter. The sensor is usually very close by. It's a relatively small sensor with one or two wires connected to it. Look for a sensor with a single wire going to it (this is the most likely candidate for your oil pressure gauge).
Troubleshooting the intermittent high reading:
* Check the wiring: Inspect the wiring harness leading from the sensor to the gauge for any damage, loose connections, or short circuits. Pay close attention to the connectors.
* Test the sensor: You can test the sensor's resistance with a multimeter (following the instructions in your repair manual). This helps determine if the sensor is faulty. However, the intermittent nature makes this less conclusive.
* Test the gauge: If the wiring to the sensor checks out, the gauge itself might be faulty. A mechanic can test the gauge's operation.
Important Note: Before attempting any repairs yourself, ensure the engine is cool and disconnect the negative battery terminal to prevent accidental short circuits. If you're not comfortable working on your vehicle's engine, take it to a qualified mechanic for diagnosis and repair. A faulty oil pressure reading could indicate a serious engine problem, so it's best to get it checked professionally if you can't pinpoint the cause.
