How to Read MAP Sensor Voltage on 1999 S-10 with P0107, P0108, and P0200 Fault Codes

OBDwiz scanners vary in functionality—make sure you're using the correct mode. Please post all fault codes along with a detailed description of symptoms so others can provide accurate advice.

I have P0107, P0108, and P0200. The truck died while driving. It now starts but runs very rough and doesn't respond to throttle input.

P0107, P0108, and P0200—these codes suggest a possible wiring issue such as damaged harnesses, shorts, or grounding problems. Have there been any recent repairs, flooding, or accidents? For P0200 (all injectors malfunction), unplug each injector and check for 12V at the injector terminals with the key off (KOEO). Confirm which wire has power. To test the MAP sensor, connect a voltmeter to the center terminal while the sensor is plugged in.

I recharged the battery, cleared the codes, and the truck started—but still ran poorly. The OBDwiz tool showed normal MAP sensor readings. When I tested the injectors with KOEO, no voltage was detected on any of them.

No 12V at injector wires during KOEO? Check the underhood fuse box—verify fuses by testing both sides of the terminals. Also inspect the fuel pump relay; it may time out after about 2 seconds if the engine isn't running. Note: The injector gray wire typically carries 12V from the relay. Fuse ECM-B is likely a 20-amp fuse.

I recently replaced the fuel filter and checked fuel pressure—no issues found. I retested the injectors with KOEO, still no voltage (the rear injector wire was difficult to access). The ECM-B fuse tested at 11.9V to ground and 7.8V across—it is good per ohmmeter reading.

All injectors share the same 12V source via the gray wire—let’s focus on accessible injectors first. The fuel pump relay supplies power to injectors, but only for about 2 seconds if the engine isn’t running. This means voltage may not be present during testing unless you're quick. When unplugged, the injector's other wire should show no voltage and remain open (not grounded). I’ll share a wiring diagram when available.

I replaced the spark plug wires, but that was after the problem began—so it’s not likely related to ignition components.

With help from someone else, I cycled the key and measured only 0.01V at the injector terminals—this suggests a possible issue with power delivery or ground connection.

Should I inspect the fuel pump relay itself and its wiring connections for continuity and proper operation?

Wait—on my last test, I had not reinserted the ECM-B fuse. After doing so, I now have near 12V at all injectors.

Now check the other injector wire: is it grounded? Is it open? Use a test light to connect between the two wires—does it illuminate? If so, try starting the engine and observe if the light blinks or stays off.

Thanks, Kev2. I’m dealing with real-world issues right now—I’ll check these connections tomorrow.

Finally got time to work on this. I used a noid light and tested all four injector circuits—each flashed when the engine was turned over, indicating proper signal. This suggests injectors are functioning correctly. However, fuel pressure drops immediately to zero when the ignition is turned off—is this normal or could it point to a faulty fuel pressure regulator?