1996 Chevy C2500 5.7L Engine P0102 Fault: Diagnosing Blown Fuse and Sensor Issues

I agree that troubleshooting this issue can be time-consuming, but it's manageable with proper methodology. I redid the wiring splice and extended the wire lengths for better access. Additionally, I replaced the MAF sensor plug. After these steps, the check engine light did not return. At one point, simply turning the key on caused a fuse to blow—this indicated a potential short in the ignition circuit. To resolve this, I plan to systematically test each circuit by disconnecting connectors and observing if the fuse blows when the ignition is turned on. With over 20 years of experience working on helicopters, I’ve learned that difficult problems are often more interesting than easy ones. I’ll keep others updated as progress is made.

The issue remains unresolved. I rechecked every wire in the harness and replaced the fuse—no check engine light appeared, and I drove the vehicle five to six times over short distances without any issues. However, after driving approximately 20 miles, the engine fuse blew again. This suggests a component may be overheating or causing a load surge. I suspect a sensor is generating excessive voltage under load conditions. I plan to perform a cold start test and monitor if the fuse blows when the vehicle is cold. At this point, I’m beginning to consider that the PCM/ECM might be failing—though this remains speculative. Any insights would be greatly appreciated.

You cannot simply assume a timing adjustment fixes issues—loosening the distributor bolt and rotating it does change timing, but proper system understanding is essential before making recommendations. For instance, verifying camshaft position at 1000 RPM with ±2 degrees tolerance is critical. A low-resistance ohm reading doesn’t guarantee circuit integrity. To test circuits accurately, use a halogen headlight bulb with alligator clips: one end connects to the battery terminal, and the other to the circuit under test. Test for 10–20 seconds. For example, if a fuel pump circuit has only a tiny wire fragment left or corroded relay contacts, an ohmmeter may show near-zero resistance when disconnected from the battery—but it will fail during load testing (like when the fuel pump tries to run). This is why real-world load testing is essential. I’ve worked extensively in GM technical support and diagnostics—this approach helps identify hidden faults others miss.

Two effective methods exist for diagnosing this issue: disconnect each sensor one at a time to see if the fuse blows, or install inline 10A fuses on each component’s circuit and observe which one fails. The P0102 code is not the root cause—instead, focus on the blown fuse, as it powers multiple components including EVAP purge solenoid, EGR valve, MAF sensor, B1S1/B1S2/B2S1/B2S2 oxygen sensors, and VCM/ECM. Exclude CMP and VCM/ECM from inline testing due to their critical role. My best guess is the EVAP purge system—this is a common failure point. The MAF code (P0102) may be secondary, as it typically appears during stalling events. Prioritize diagnosing the blown fuse circuit to locate the actual fault source.

We’ve now replaced both front O2 sensors (Bank 1 and Bank 2), confirmed correct part numbers for a manual transmission, and installed a new PCM programmed specifically for this vehicle. After driving several miles, the check engine light reappeared with code P151—indicating an oxygen sensor signal issue. This has created confusion as we’ve already addressed potential sensor faults. I’m now unsure whether the original fuse problem is related or if it’s a separate failure in the feedback loop. Any guidance on interpreting this new error would be greatly appreciated.

The only current code is P0151—no exhaust leaks detected. The PCM reports low voltage return (200mV or less than 350mV) on the B2S1 oxygen sensor (passenger side, first sensor). This suggests a wiring issue or faulty signal. Using a scan tool to monitor readings is recommended. To test functionality, simulate a rich condition by spraying carb cleaner into the throttle body and partially blocking airflow—this should cause the voltage at the sensor’s low-side terminal (tan wire) to increase. If it does, the sensor is responsive; if not, there may be a wiring or internal fault.

I partially understand your explanation but need clarification. I’m considering checking the wiring from each oxygen sensor directly to the computer plug as a practical next step. I have a wiring diagram that shows which wires connect to which sensors—this seems like a reliable way to verify signal integrity. My assumption is that I can measure voltage at this connection point and validate it against expected values. While I typically work in volts, I’m not confident in interpreting millivolt-level signals. My brother, who is an electronics expert from Michigan and will be visiting on Friday, will assist with testing. I’ll update the community as soon as we have results.

The most likely cause is a wire or wires that are pinched or damaged due to movement. Try relocating each wire and see if the issue reoccurs—this can help confirm whether mechanical stress is causing intermittent faults.