Technical Description of OBD-II Trouble Code
The engine is experiencing intermittent/erratic pulses in the Timing Reference High Resolution Signal B.
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code that applies to OBD-II equipped vehicles with an engine position sensor (Chevrolet, GMC, Ford, Dodge, BMW, etc.). While it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
The powertrain control module (PCM) relies on a timing reference signal to determine the engine’s speed and position. This signal is provided by an engine position sensor, such as a crankshaft, camshaft, or fuel pump position sensor.
The PCM uses this information to control fuel injector operation, ignition timing, and diagnose misfires. There are two main types of engine position sensors: Hall-Effect and permanent magnet sensors.
Both types of sensors are triggered by a wheel or disc located near the sensor. Common mounting locations for the wheel/disc include the engine position, injection pump, harmonic balancer, and distributor shaft. When triggered, the sensor sends a return signal back to the PCM.
In the codes mentioned in this article, the “B” indicates that the issue is with a portion of the system circuit, rather than a specific symptom or component.
A code P0378 is set when the PCM detects intermittent/erratic pulses in the engine position sensor “B” signal.
Other related trouble codes for the timing reference signal B include:
Code Severity & Symptoms
The severity of these codes ranges from moderate to severe. Symptoms of a P0378 engine code may include:
Causes
Possible causes for this P0378 code include:
Diagnostic and Repair Procedures
Begin by visually inspecting the engine position sensor and its wiring. Look for loose connections, damaged wiring, or any other visible issues. If any damage is found, repair it as necessary, clear the code, and check if it returns. Additionally, inspect the engine for any metal particulates that could affect sensor operation.
Next, check for any technical service bulletins (TSBs) related to this issue. If no relevant TSBs are found, proceed with step-by-step diagnosis of the system.
The following is a general procedure, as testing for this code can vary between vehicles. For accurate testing, refer to the manufacturer’s diagnostic flow chart. The specific test procedures also depend on the type of sensor in your vehicle.
Check the sensor
Hall-Effect sensor: Use a digital multimeter set to DC volts and a back-probe test lead to verify that the sensor is producing a signal voltage. Connect one meter lead to the sensor signal wire and the other to ground. Have an assistant tap the ignition key (without starting the engine) to rotate the engine; the voltage reading should fluctuate between 0 volts and the reference voltage. If available, you can also use an oscilloscope to view the signal pulses while cranking the engine.
Permanent magnet sensor: Start by checking the internal resistance of the sensor. Disconnect the sensor electrical connector and use a digital multimeter set to ohms to measure the resistance between each of the sensor terminals. The resistance should be approximately 500 to 1,200 ohms. Consult the factory repair information for the exact specification. If the resistance test is within range, proceed to test the sensor performance. Reconnect the sensor electrical connector and use a digital multimeter set to AC volts to measure the sensor’s AC voltage output. Since the sensor produces AC voltage, it doesn’t matter which way the meter leads are connected. Have an assistant crank the engine; you should observe a fluctuating voltage reading.
During sensor testing, keep in mind that a damaged or improperly aligned tone ring can prevent proper sensor operation. If in doubt, access the tone ring and inspect it as needed.
Check the circuit
It is recommended to have the factory wiring diagram available to determine which wire is which during these tests.
Hall-effect sensor:
Permanent magnet sensor:
