Diagnostic Code P0373: Engine Position Sensor “A”
What Does It Mean?
Diagnostic Trouble Code (DTC) P0373 is a generic powertrain code applicable to OBD-II equipped vehicles with an engine position sensor (Chevrolet, GMC, Ford, Dodge, BMW, etc.). Although generic, repair steps may vary depending on the vehicle’s make and model.
The Powertrain Control Module (PCM) requires a timing reference signal to determine engine speed and position. This is made possible through an engine position sensor, such as a crankshaft position sensor, camshaft position sensor, or fuel pump sensor.
The PCM uses this information to manage:
- Fuel injector control,
- Ignition timing,
- Misfire diagnosis.
There are two main types of engine position sensors:
- Hall effect sensors,
- Permanent magnet (PM) sensors.
These sensors are triggered by a wheel or disk mounted nearby. They send a feedback signal to the PCM, which interprets it to adjust engine operation.
In the case of code P0373, the “A” indicates that the problem is related to a part of the system circuit rather than a specific component. The code is set when the PCM detects an intermittent or erratic signal from engine position sensor “A”.
Code Severity and Symptoms
The severity of code P0373 ranges from moderate to severe. Common symptoms include:
- Illuminated check engine light,
- Difficulty starting or failure to start,
- Poor engine performance.
Possible Causes
Potential causes of this code are:
- Faulty sensor,
- Wiring issues,
- Damaged reluctor wheel,
- Contaminated oil,
- Faulty PCM.
Diagnostic and Repair Procedures
1. Visual Inspection
- Check the engine position sensor and its wiring.
- Look for loose connections or damaged wires.
- If damage is detected, perform necessary repairs, clear the code, and see if it returns.
- Ensure the engine does not contain metal particles that could affect the sensor.
2. Checking Technical Service Bulletins (TSBs)
- Consult TSBs to see if there are specific recommendations for your vehicle.
- If no relevant TSBs are found, proceed with detailed diagnosis.
3. Sensor Testing
Hall Effect Sensor
- Set a digital multimeter to DC volts.
- Probe the sensor’s signal wire and ground.
- Turn the ignition key without starting the engine.
- The reading should fluctuate between 0 volts and the reference voltage (usually 5V).
- An oscilloscope can also be used to visualize signal pulses.
Permanent Magnet (PM) Sensor
- Check the sensor’s internal resistance (should be between 500 and 1,200 ohms according to manufacturer specifications).
- Connect a digital multimeter in AC volts to the sensor connector.
- Start the engine and check for fluctuating voltage readings.
Note: A damaged or misaligned tone ring can cause sensor malfunction.
4. Circuit Testing
Having the manufacturer’s wiring diagram is recommended to correctly identify wires.
Hall Effect Sensor
- Check circuit ground:
- Multimeter in ohms mode between the connector’s ground terminal and earth.
- If the reading is out of limits (OL), there is an open circuit to repair.
- Check reference voltage:
- Ignition on, measure the reference voltage (usually 5V) between the sensor and PCM.
- If no voltage is present, there is an open circuit to identify and repair.
- Check return signal:
- Ignition off, multimeter in ohms mode between the sensor output and PCM.
- If the reading is out of limits (OL), there is an open circuit to repair.
Permanent Magnet (PM) Sensor
- Check circuit ground:
- Multimeter in ohms mode between the sensor’s ground terminal and earth.
- If OL is displayed, an open circuit is present and must be repaired.
- Check return signal:
- Multimeter in ohms mode between the sensor output and PCM.
- An out-of-limits (OL) reading indicates an open circuit requiring repair.
Conclusion
Code P0373 is often related to an erratic signal from the engine position sensor. A methodical diagnosis involving visual inspection, sensor testing, and circuit verification is essential to effectively identify and correct the problem.