Error Code P0378: What It Means & What To Do?

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Diagnostic Trouble Code P0378 is defined as Timing reference, high resolution signal B – intermittent/erratic pulses wherein the “B” pertains more to an area of the system circuitry than to a particular component. P0378 means the high-resolution timing reference signal B is pulsing abnormally, indicating a faulty circuit in the system. This code is detected when some high-resolution pulses are intermittent from the optical sensor to the PCM.

OBD-II Code Decreased engine performance is defined as a Timing Reference High Resolution Signal "B" Intermittent/Erratic. A code P0378 is set when the PCM detects the engine position sensor "B" is producing a signal with intermittent/erratic pulses. The optical sensor provides a high-resolution signal to the Powertrain Control Module (PCM) by counting pulses on the sensor disk located in the injection pump. The high resolution is one of the most important inputs by the PCM for fuel control and timing. The PCM tests for missed pulses, and compares those to the number of pulses it should be detecting according to the manufacturer. If this value is not correct or erratic, the PCM will store the code P0378. he maximum allowable number of degrees of variation may differ between manufacturers, vehicle lines, engine sizes/types, and transmission applications.

What causes this problem with the Timing Reference High Resolution Signal B Intermittent/Erratic Pulses?

• Defective Sensors (Crankshaft, Camshaft or Distributive Position Sensor)
• Frayed distributor
• Optical sensor is shorted
• Damaged wiring or connectors
• PCM failure

1. Powertrain Control Module - The Powertrain Control Module (PCM) is the electronic brain that controls almost everything the engine (and transmission in many cases) does.
2. Optical Sensor - An optical sensor converts light rays into an electronic signal. The purpose of an optical sensor is to measure a physical quantity of light and, depending on the type of sensor, then translates it into a form that is readable by an integrated measuring device.
3. Camshaft Position Sensor - The camshaft position sensor gathers information about the vehicle's camshaft speed and sends it to the vehicle's engine control module (ECM).
4. Crankshaft Position Sensor - A crank sensor is an electronic device used in an internal combustion engine, both petrol and diesel, to monitor the position or rotational speed of the crankshaft.

Please note that it may take a while before your service engine light comes on, so it is important to recognize these other symptoms ahead of time. Knowing these symptoms will help you fix it quickly.

• Falling engine performance
• Engine may not start
• Decreased fuel mileage
• Spark knock upon acceleration
• Illuminated check engine light

P0378 code relates directly to how the PCM controls fuel injection and timing, this is a very serious issue that should be resolved immediately else it may result in the failure of other engine components when they would not be able to obtain fuel, or correct fuel pressure. Following repairs and replacements can help you fix this code:

• Repair or replace the faulty crankshaft, crankshaft gear, crankshaft position sensor, and the sensor connector
• Repair or replace faulty camshaft components
• Repair or replace a faulty mechanical distributor
• Repair or replace an open or shorted optical sensor
• Repair or replace faulty, corroded, damaged, open, or shorted wiring or connectors
• Check and replace faulty crank and cam reluctor rings
• Replace the faulty PCM (Rare)

All the above-mentioned components need to be perfect in order to avoid the error code P0378. If ever you discover them malfunctioned, repair or replace them as required. On Parts Avatar Canada you will find them on best possible prices. Click now to check them out.

Here are some steps which one should follow in order to diagnose this P0378 fault code:

• Verify your crankshaft position sensor to check for an engine RPM signal when the engine is cranked or running by using scanner or a tachometer.
• If in case you do not detect an RPM signal, then visually inspect the crankshaft position sensor, crankshaft gear, and sensor connector for damage and signs of repair.
• Test the CPS system for a reference voltage signal (typically five-volts).
• Check for system continuity using your digital volt/ohmmeter.
• Disconnect the electrical connector from the PCM before using your ohmmeter on the harness side of the circuit.
• Note: There is a test drive recommended after you've completed any repairs to see if the condition is fixed. Before you take a test drive after a repair, always erase the P Code(s) first. This will turn the check engine light off and then you will know if the check engine light returns, you've got further diagnostics to complete.

Common Mistakes When Diagnosing the P0378 Code

The most common mistake while diagnosing this code is unnecessary replacement of crankshaft, camshaft, and distributor sensors, when mechanical distributor failure is the main cause setting this code.