OBD-II Code P0370 — What It Means & How to Fix It

What Does This Error Mean?

P0370 means the PCM detected a problem with the high-resolution timing reference signal A. This is a secondary timing signal — used on some engines alongside the standard crankshaft and camshaft position sensors — that provides very precise engine position data for accurate fuel and ignition timing. A fault here can cause hesitation, rough running, misfires, and reduced performance.

Affected Models

Vehicles with high-resolution timing sensor systems — most common in older GM vehicles
Common in GM trucks and SUVs from the late 1990s and early 2000s
Common in some older Ford and Chrysler vehicles with secondary timing reference signals
Less common on modern vehicles where the main CKP/CMP sensors handle all timing data
More likely on high-performance or truck engines where precise timing is critical

Common Causes

Failed or weak high-resolution timing sensor producing an unreliable signal
Damaged or broken wiring in the timing reference sensor circuit
Loose or corroded connector at the high-resolution timing sensor
Debris or buildup on the sensor tone wheel interrupting the signal pattern
Incorrect air gap between the sensor and the tone wheel

How to Fix It

Research where the high-resolution timing reference sensor A is located on your specific vehicle. On older GM trucks it is often part of the distributor assembly or mounted near the crankshaft. Your factory service manual will have the exact location and wiring diagram.

P0370 is more common on vehicles from the late 1990s and early 2000s. Modern vehicles are less likely to have a separate high-resolution timing signal sensor. Confirm whether your vehicle actually uses this type of sensor before spending time searching for it.
Inspect the sensor connector and wiring. Look for corrosion, physical damage, or a loose connection. Clean the connector with electrical contact cleaner and reseat it firmly. Wiggle the harness while checking for any change in fault behavior.

On older vehicles, corroded connectors are one of the most common causes of timing sensor faults. A thorough cleaning and reseating of the connector sometimes resolves the code without any part replacement.
Check the air gap between the sensor and the tone wheel or reluctor ring. The gap must be within manufacturer specification — usually 0.5 to 1.5 mm depending on the application. An incorrect gap will cause a weak or missing signal.

If the sensor mounting bracket was disturbed during other repair work, the air gap can be off even with the original sensor. Always verify the gap after any work in the area.
Inspect the tone wheel for missing or damaged teeth, metal debris bridging two teeth, or buildup of ferrous material that would distort the magnetic field. Clean the reluctor ring carefully if debris is present.

A single missing or damaged tooth on the tone wheel will cause a signal dropout at the same point in every engine revolution. A lab scope showing the signal pattern can reveal this quickly.
Replace the high-resolution timing sensor A if it has failed. Install the new sensor at the correct air gap. Clear all codes and road test. If P0370 returns, have a technician scope the sensor output pattern to check for any irregularities in the signal waveform.

After replacement, verify the air gap again with a feeler gauge before buttoning everything up. Getting the gap right the first time prevents a repeat diagnosis.

When to Call a Professional

P0370 is less common on modern vehicles and can require manufacturer-specific documentation to locate the high-resolution timing sensor. If sensor replacement and wiring repair do not clear the code, a technician with factory service data and a lab scope can verify the signal pattern. Diagnosis typically costs $80-$150. Sensor replacement parts cost $30-$100 depending on the application.

Frequently Asked Questions

What is a high-resolution timing reference signal?

Some engines use two levels of timing signals. The standard crankshaft and camshaft sensors give the PCM basic engine position data. A high-resolution timing signal provides much finer detail about exactly where the pistons are in their cycle — down to just a few degrees of crankshaft rotation. This extra precision allows for more accurate fuel injection timing and ignition advance, especially at high RPM.

Is P0370 common on modern cars?

No, it is mostly a code from older vehicles — particularly late 1990s and early 2000s GM trucks and cars. Modern engine management systems use the standard crankshaft and camshaft position sensors with enough resolution to eliminate the need for a separate high-resolution signal. If you have a modern vehicle, P0370 is unlikely — double-check the code.

Can P0370 cause a no-start?

It can, particularly if the high-resolution signal is the primary timing reference the PCM relies on for fuel injection. More commonly it causes poor performance, misfires, and drivability problems while the engine still runs. On some older GM vehicles, a complete loss of this signal will prevent starting.