OBD Codes
Your OBD-II Trouble Codes Repair Site

P0377 Timing Reference High Resolution Signal B Too Few Pulses

OBD-II Trouble Code Technical Description

Article by
Mia
Mia B.
ASE Certified Master Technician

Timing Reference High Resolution Signal B Too Few Pulses

What does that mean?

This diagnostic trouble code (DTC) is a generic powertrain code, which means it applies to OBD-II equipped vehicles which have an engine position sensor (Chevrolet, GMC, Ford, Dodge, BMW, etc.). Although generic, the exact repair steps may vary depending on 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, camshaft or fuel pump position 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 positions sensors: Hall-Effect and permanent magnet.

Both types of sensors are triggered by a wheel or disc mounted close to 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 which is sent back to the PCM.

In the codes outlined in this article, the "B" indicates the problem is with a portion of the system circuit, instead of a particular symptom or component.

A code P0377 is set when the PCM detects the engine position sensor "B" is producing a signal with too few pulses.

Related timing reference signal B trouble codes include:

Code Severity & Symptoms

The severity of these codes is moderate to severe. Symptoms of a P0377 engine code may include:

Causes

Possible causes for this P0377 code include:

Diagnostic and Repair Procedures

Begin by visually inspecting the engine position sensor and the corresponding wiring. Look for loose connections, damaged wiring, etc. If damage is found, repair as necessary, clear the code and see if it returns. Also, check the engine for any metal particulates that may affect sensor operation.

Next, check for technical service bulletins (TSBs) regarding the issue. If nothing is found, move forward to step by step diagnosis of the system.

The following is a generalized procedure, as testing for this code varies between vehicles. To accurately test the system, you'll want to refer to the manufacture's diagnostic flow chart. Test 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 signal wire and the other to ground. Have an assistant rotate the engine by tapping the ignition key (don't start the engine); the voltage reading should fluctuate between 0 volts and reference voltage. If available, you can also use an oscilloscope to view the signal pulses while cranking the engine.

Permanent magnet sensor: begin by checking the internal resistance of the sensor. Disconnect the sensor electrical connector and connect a digital multimeter set to ohms to 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 OK, you'll want to test the sensor performance. To do this, reconnect the sensor electrical connector. Then, connect a digital multimeter set to AC volts to the sensor electrical connector using back probe test leads. Since the sensor produces AC voltage, is doesn't matter which way the meter leads are connected. Have an assistant crank the engine; you should see a fluctuating voltage reading.

One thing to remember during sensor testing damaged or improperly aligned tone ring will prevent proper sensor operation. When in doubt, access the tone ring and inspect as needed.

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:

Permanent magnet sensor:

Related P0377 DTC Discussions

Need more help with a p0377 code?

If you still need help regarding the P0377 trouble code, please post your question in our FREE car repair forums.

NOTE: This information is presented for information purposes only. It is not intended as repair advice and we are not responsible for any actions you take on any vehicle. All information on this site is copyright protected.