1997 Chevrolet 1500 P0340 Camshaft Position Sensor Fault: Is 1V Output Normal? Diagnosing PCM vs. Sensor Issues

The expected signal voltage during engine operation should be 5–7 volts DC, not 1 volt. Let's start with basic wiring checks: 1) Terminal C (pink wire): Is there a solid 12V supply? 2) Terminal A (pink/blk): Is the ground connection good? Use a test light between terminals A and C to verify. 3) Terminal B (brn/wht): Should read 5–7 volts when engine is running. If only 1 volt is measured, this indicates a problem. Check for continuity between sensor terminal B and PCM terminal C1 (wiring harness). Common failures occur in the first 3 inches of wiring—look for: • Backed-out terminals • Improper connector mating • Broken or damaged terminal locks • Poor wire-to-terminal connections • Physical damage to the harness. Ensure all connectors are properly seated and clean.

Are you measuring voltage on terminal B when the engine is running with a multimeter (DC voltage) or using an oscilloscope? Some sources indicate that 12V may be observed at ignition-on without engine movement, but this does not reflect normal operating conditions. I’ve confirmed that the sensor-to-PCM wiring connection is intact and properly attached. The sensor receives 12V at terminals A and C. Could a failing PCM be causing the signal to drop to 1 volt? This seems plausible, but we need further verification.

During engine operation, the expected voltage should be 5–7 volts DC. While a faulty PCM could cause low output (e.g., 1V), it's important to verify this before concluding PCM failure. Before blaming the PCM, perform an ohm resistance test between the sensor and the PCM wire (brn/wht). This will help confirm whether the issue lies in the wiring or the sensor itself. Also, check the freeze frame data—this may reveal engine conditions at fault occurrence.

Hi, thanks for the input. I've tested the resistance between the sensor and PCM wire (brn/wht) and it reads fine. I didn’t check freeze frame data—will that help identify the fault condition? I’ve now reached about 90% confidence that the issue is with the PCM. Since the sensor is receiving 12V at terminals A and C, and I’m getting only a 1-volt signal on terminal B, I wonder if there’s a simple test: connect 12V to terminals A and C (power and ground) while applying an uninterrupted signal to the sensor—should this produce 12V between terminals A and B? If not, does that point to a faulty sensor or PCM?

Terminals A and C should show 12V when powered. Terminal A is power, terminal C is ground. With the engine running, what voltage do you read on terminal B? A reading of 1 volt is incorrect—this does not match expected sensor output.

When the engine is running, terminal B reads only 1V. This contradicts OEM specifications. I’ve been told it should be either 12V or between 6–7V. I need to test the sensor independently of the PCM to rule out a faulty signal path caused by the PCM. Since my AC Delco replacement sensor also produces only 1V, and this is an aftermarket unit, I suspect the issue may not be with the sensor itself—but could it still be a PCM-related short? If the PCM is causing a drop in voltage, testing the sensor off-vehicle would help confirm whether the sensor is functioning correctly or if the fault originates at the PCM end of the circuit.

Double-check all diagnostic steps. A key test involves analyzing the signal duty cycle (in hertz) to assess sensor performance. There appear to be two different trouble trees for this engine model—some sources list 5–7V, others suggest 12V. I’m still trying to reconcile why there are conflicting specifications and need to verify which one applies correctly to the 1997 Chevrolet 1500.

I don’t believe it's common for a PCM to fail—many technicians assume this without proper diagnostics. Always perform basic electrical checks before replacing a PCM. A faulty circuit could be due to corrosion, wire damage (e.g., chewed by rodents), or oxidation in connectors. If sensor replacements and wiring checks are complete but the issue persists, then the PCM is likely at fault. I recently replaced my 1997 Chevrolet PCM with a pre-flashed unit from Flashmasters.com (over 185 units sold)—this issue is not rare. After replacement, both P0340 and an unrelated auto transmission slippage issue resolved. If you're experiencing similar issues with your 1997 Chevy PCM, consider that the module may be faulty.

85–90% of reported 'faulty' ECMs are actually functional. Most recurring failures stem from terminal fretting—poor connections or corrosion. Technicians often install a new sensor, relay, or PCM and assume the issue is fixed. Days later, it returns—or worse, customers blame them for spending $600 on parts that didn’t solve the real problem. In such cases, the root cause is usually terminal degradation—such as loose connections or lack of dielectric grease. So, don't jump to conclusions about a failing PCM. Always inspect connectors and apply dielectric grease when reassembling. (Former GM Tech Support Engineer; currently works at a GM Tech Center specializing in complex engine diagnostics.)

Don’t assume circuits are good just because an ohm test shows low resistance. For example, if a 12-strand wire has 11 strands chewed through (common with rodents or ground hogs), the ohmmeter may show near-zero resistance—but the circuit is still broken. A corroded relay or coolant-contaminated connection can also cause false readings. To avoid such misdiagnoses, use a halogen headlamp bulb or blower motor to test power circuits. Solder 4–5 feet of wire to each lead and attach alligator clips. For power testing, connect the ground clip to a known good ground (preferably battery negative). This method ensures accurate circuit integrity checks—especially when diagnosing sensor or PCM issues.