Quick answer: The P0373 code indicates that the engine control module detected erratic or intermittent high-resolution timing signals from reference sensor ‘A’. Affecting the ignition and fuel delivery system, this is a serious issue that can cause engine stalling or a complete no-start condition, requiring prompt inspection.
Seeing code P0373 pop up on your scan tool usually comes with noticeable engine hesitation or sudden stalling. This diagnostic trouble code points directly to an erratic timing reference signal that your vehicle’s computer relies on to coordinate fuel injection and spark timing. In this guide, we will break down what causes this signal disruption, how to spot the symptoms, and the step-by-step diagnostic process to fix it.
What Does P0373 Mean?
The P0373 code stands for “Timing Reference High Resolution Signal ‘A’ Intermittent/Erratic Pulses.” Your engine control module (ECM) relies on high-resolution timing pulses to determine the exact position and rotational speed of the engine. This signal-often generated by an optical or magnetic sensor inside the distributor or mounted on the crankshaft-provides precise data down to fractions of a degree. When the ECM detects missing, extra, or irregular pulses in signal ‘A’, it loses its ability to sequence ignition timing and fuel delivery accurately, triggering the check engine light and safeguard protocols.
Symptoms
- Engine stalling or unexpected shutting off while driving
- Hard starting or a complete engine no-start condition
- Severe engine misfires, rough idling, or stumbling during acceleration
- Illuminated Check Engine Light on the dashboard
- Loss of engine power and noticeable hesitation under load
Possible Causes
A common mistake when diagnosing P0373 is replacing expensive sensors or entire distributor assemblies before checking the basic wiring and ground connections that frequently degrade over time.
- Damaged, corroded, or loose wiring harness connections at the timing sensor
- Faulty timing reference sensor (optical, crankshaft, or camshaft position sensor)
- Electrical interference from nearby high-voltage ignition components or bad engine grounds
- Debris, metal shavings, or engine oil buildup contaminating the sensor lens or tone ring
- Failing Powertrain Control Module (PCM/ECM) or outdated engine management software
Check These Yourself Before Visiting a Mechanic
- Inspect the sensor wiring connector for loose pins, green corrosion, moisture, or melted wire insulation near exhaust components.
- Check main ground connections around the engine block and firewall to ensure tight, clean contact free of rust or oil.
- Examine the area around the sensor for active oil leaks or heavy dirt build-up that could physically block the sensor signal.
How to Fix It
- Perform a thorough visual inspection of the timing sensor harness and connectors for physical damage.
- Clear the trouble code using an OBD-II scanner and conduct a road test to see if the intermittent signal returns.
- Test circuit continuity, reference voltage, and ground signal at the sensor connector using a digital multimeter.
- Inspect the internal timing disk, tone ring, or sensor lens for optical blockage, mechanical damage, or oil contamination.
- Monitor live timing signal data with a diagnostic oscilloscope or high-end scan tool to verify erratic pulse drops.
- Replace the faulty timing reference sensor or repair damaged wiring as needed.
Estimated Repair Costs (2026)
| Job | Parts ($) | Labor ($) |
|---|---|---|
| Wiring Repair / Harness Cleaning | $15 – $50 | $100 – $200 |
| Timing Reference / Position Sensor Replacement | $50 – $180 | $100 – $250 |
| Distributor Assembly Replacement (if applicable) | $150 – $450 | $120 – $250 |
Note: These are 2026 estimates in US dollars; costs vary by make and model.
Frequently Asked Questions
Can I drive with the P0373 code?
It is not recommended to drive with this code active. Because P0373 indicates an erratic timing signal, the engine can stall suddenly without warning, creating a potential safety hazard in traffic.
How do I clear the P0373 code?
You can clear the code using any standard OBD-II scan tool after addressing the underlying issue. If the signal fault remains unresolved, the engine control module will set the code again shortly after starting the engine.
What causes the timing signal to become intermittent?
Intermittent signals are most commonly caused by thermal expansion affecting weak electrical connections, dirty optical sensor lenses, loose engine ground straps, or electromagnetic interference from worn ignition components.