What does it mean?
This diagnostic code (DTC) is a generic powertrain code, meaning it applies to OBD-II equipped vehicles that have an engine position sensor (Chevrolet, GMC, Ford, Dodge, BMW, etc.). Although generic, the exact repair steps may vary by make/model.
The Powertrain Control Module (PCM) requires a timing reference signal to determine engine speed and position. This is accomplished by means of an engine position sensor, such as a crankshaft position sensor, camshaft position sensor, or fuel pump sensor.
The PCM uses this information to determine one or more of the following: fuel injector control, ignition timing, and misfire diagnostics. There are two basic types of engine position sensors: Hall effect and permanent magnet.
Both types of sensors are triggered by a wheel or disc mounted near the sensor. Typical wheel/disc mounting locations include the engine position, injection pump, harmonic balancer, and distributor shaft. When triggered, the sensor produces a return signal that is sent back to the PCM.
Hall effect crankshaft position sensors have three wires: reference (power), signal, and ground. The sensor receives a reference voltage (usually 5 volts) from the PCM and is triggered by a reluctor wheel. The sensor then sends a corresponding digital return signal to the PCM.
Permanent magnet (PM) sensors produce their own alternating voltage based on their proximity to a rotating reluctor wheel. This voltage signal is sent back to the PCM where it is converted into a digital signal by an internal analog-to-digital converter.
In the codes described in this article, the “A” indicates that the problem is with a part of the system circuit, rather than a specific symptom or component.
A P0372 code is set when the PCM detects that the engine position sensor “A” is producing a signal with too few pulses.
Code Severity and Symptoms
The severity of these codes is moderate to severe. Symptoms of a P0372 engine code may include:
Illuminated check engine light
Hard starting / no start
Poor engine performance
Causes
Possible causes of this P0372 code are as follows:
Faulty sensor
Wiring problems
Damaged reluctor wheel
Contaminated oil
Faulty PCM
Diagnostic and Repair Procedures
Start by visually inspecting the engine position sensor and its corresponding wiring. Look for loose connections, damaged wiring, etc. If damage is detected, repair as necessary, clear the code, and see if it returns. Also check that the engine does not contain any metal particles that could affect the sensor’s operation.
Next, check for technical service bulletins (TSBs) regarding the issue. If nothing is found, proceed with step-by-step system diagnostics.
The following is a generalized procedure, as tests for this code vary by vehicle. To accurately test the system, you will need to refer to the manufacturer’s diagnostic flowchart. Testing procedures also depend on the type of sensor found in your vehicle.
Check the Sensor
Hall effect sensor: Use a digital multimeter set to DC volts and a back-probe test lead to ensure the sensor is producing a signal voltage. Connect one meter lead to the sensor’s signal wire and the other to ground. Have an assistant crank the engine by turning the ignition key (do not start the engine); the voltage reading should fluctuate between 0 volts and the reference voltage. If available, you can also use an oscilloscope to visualize the signal pulses while starting the engine.
Permanent magnet sensor: Start by checking the sensor’s internal resistance. Disconnect the sensor’s electrical connector and connect a digital multimeter set to ohms to each of the sensor’s terminals. The resistance should be approximately 500 to 1,200 ohms. Consult factory repair information for exact specifications. If the resistance test is OK, you will want to test the sensor’s performance. To do this, reconnect the sensor’s electrical connector. Then, connect a digital multimeter set to AC volts to the sensor’s electrical connector using back-probe test leads. Since the sensor produces an alternating voltage, it does not matter how the multimeter leads are connected. Have an assistant start the engine; you should see a fluctuating voltage reading.
One thing to remember when testing the sensor is a damaged or misaligned tone ring that will prevent the sensor from functioning properly. If in doubt, access the tone ring and inspect it if necessary.
Check the Circuit
It’s a good idea to have the factory wiring diagram on hand to determine which wire is which while performing these tests.
Hall effect sensor:
Check the ground side of the circuit: Connect the ohmmeter (ignition off) between the sensor connector’s ground terminal and ground. If the meter reads out of limits (OL), there is an open circuit on the ground side of the circuit, which must be located and repaired. If the meter reads a numerical value, there is continuity.
Check the reference voltage side of the circuit: With ignition on, use a digital multimeter set to volts to check for the PCM reference (usually 5 volts) at one of the sensor’s three terminals. If no reference signal is present, connect the ohmmeter (ignition off) between the reference voltage terminal on the sensor and the reference voltage terminal on the PCM. If the meter reads out of limits (OL), there is an open circuit between the PCM and the sensor that will need to be located and repaired. If the meter reads a numerical value, there is continuity. Then, you will want to check that there are 5 volts coming out of the PCM at the reference voltage terminal. If there is no 5-volt reference from the PCM, the PCM is likely faulty.
Check the return signal side of the circuit: With ignition off, use a digital multimeter set to ohms to check for continuity between the engine position sensor’s output terminal and the signal voltage terminal on the PCM. If the meter reads a numerical value, there is continuity. If the meter reads out of limits (OL), there is an open circuit between the PCM and the sensor that will need to be located and repaired.
Permanent magnet sensor:
Check the ground side of the circuit: Connect the ohmmeter (ignition off) between the SENSOR connector’s ground terminal and ground. If the meter reads out of limits (OL), there is an open circuit on the ground side of the circuit that will need to be located and repaired. If the meter reads a numerical value, there is continuity.
Check the return signal side of the circuit: With ignition off, use a digital multimeter set to ohms to check for continuity between the engine position sensor’s output terminal and the signal voltage terminal on the PCM. If the meter reads a numerical value, there is continuity. If the meter reads out of limits (OL), there is an open circuit between the PCM and the sensor that will need to be located and repaired.