OBD-II Code P0373 — What It Means & How to Fix It

What Does This Error Mean?

P0373 means the PCM is occasionally losing the high-resolution timing reference signal A — the signal comes and goes rather than failing completely. An intermittent timing signal causes momentary timing errors that appear as brief engine stumbles, random misfires, or an occasional stall. Because the fault is not constant, it can be one of the more frustrating codes to track down.

Affected Models

Older GM vehicles — particularly trucks and SUVs from the late 1990s through mid-2000s
Common in GM Vortec V8 and V6 powered trucks
Common in vehicles where the high-resolution sensor is in a high-vibration location
Less common on modern vehicles
More likely on aging vehicles with worn harness insulation or corroded connectors

Common Causes

Failing high-resolution timing sensor with an internal break that opens up under heat or vibration
Loose or intermittently seated harness connector at the sensor
Wire broken inside the insulation — looks fine externally but opens intermittently
Dirty or partially blocked tone wheel causing occasional missed pulses at low speed
Loose sensor mounting allowing slight movement that changes the air gap intermittently

How to Fix It

With the engine running, gently wiggle the sensor connector and the wiring harness near the sensor. Watch for any change in idle quality, misfires, or scanner data loss for the cam or crank signal. An intermittent connection will often cause a momentary stumble when the loose spot is disturbed.

Do this carefully — keep your hands away from moving parts. The wiggle test is the quickest and most practical method to find a loose or failing connection without any special tools.
Check the sensor mounting bolt or clip. A sensor that can shift even slightly in its bore will change the air gap intermittently. Tighten the mounting bolt to specification and verify the sensor does not have any side-to-side play.

On some applications, the sensor is held by a single 8mm or 10mm bolt. If this bolt is loose, the sensor can rattle and change its air gap at high vibration or high RPM.
Inspect the tone wheel surface for light debris buildup or minor corrosion that does not fully block a tooth but occasionally disrupts the magnetic field. Clean the wheel gently with a clean rag and brake cleaner.

Light surface rust or a thin film of oil residue on the tone wheel can be enough to cause intermittent signal dropouts at the exact moment a weakened tooth passes the sensor.
Replace the high-resolution timing sensor even if it looks fine externally. Internal failures that cause intermittent issues are not visible. The sensor is inexpensive relative to diagnostic labor costs, so replacing it as part of the diagnosis is a practical step.

Install the new sensor at the correct air gap and tighten the mounting bolt properly. Document the gap measurement before closing everything up.
Monitor the vehicle closely over 200-300 miles of varied driving after the repair. An intermittent fault needs extended observation time before you can confirm it is resolved. If P0373 returns after sensor replacement, pursue the wiring harness or PCM with professional help.

If the fault only appears under specific conditions — cold start, hot soak, or heavy load — try to duplicate those exact conditions during your test drive to verify the fix.

When to Call a Professional

Intermittent codes require more diagnostic time than steady codes. A technician with a lab scope can monitor the signal continuously and correlate dropouts with specific conditions — cold vs. hot, idle vs. high RPM, or harness flexing. Diagnosis for intermittent faults often takes $100-$200 in labor. A scope is genuinely necessary to catch an intermittent signal dropout that you cannot reproduce on demand.

Frequently Asked Questions

Why does an intermittent code set if the problem is not constant?

The PCM keeps a running count of how many timing errors or signal dropouts occur. Once that count exceeds a threshold — usually over a certain number of drive cycles — the PCM stores the fault code and turns on the check engine light. Even one or two brief signal dropouts per drive cycle can accumulate to trigger the code.

My car runs fine most of the time. Should I still worry about P0373?

Yes, for a few reasons. First, intermittent timing signal issues can cause brief misfires that slowly damage the catalytic converter even if you do not notice them. Second, intermittent problems tend to get worse over time rather than better. Third, any stored DTC will cause an emissions test failure. Get it investigated before it becomes a bigger or more expensive problem.

Can weather or temperature affect P0373?

Absolutely. Metal components expand and contract with temperature. A wire with a small internal break may make good contact when cold and open up when it expands with heat — or vice versa. A connector that is slightly loose may be okay in cold weather but lose contact as it warms up. If P0373 only appears after the engine is fully warm, temperature-induced expansion is likely involved.