P0379 – Timing reference, high resolution signal B -no pulses

Reinier

By Reinier (Contact Me)
Last Updated 2017-06-22
Automobile Repair Shop Owner

Trouble CodeFault LocationProbable Cause
P0379 Timing reference, high resolution signal B -no pulses Wiring, CKP/RPM/CMP sensor, ECM

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What Does Code P0379 Mean?

OBD II fault code P0379 is a generic code that is defined as “Timing reference, high resolution signal B -no pulses”, and is set when the PCM (Powertrain Control Module) detects no signals from an engine position sensor. Note that “signal/circuit B” in this definition refers to a problem in a part of the timing signal circuit, as opposed to a specific part or component.

In order for the PCM to regulate/control/determine engine speed, fuel delivery, ignition timing, and misfire diagnostic functions (among other functions), it relies on a series of signals from a sensor that measures the position of the #1 piston relative to a base setting that is in turn relative to the TDC (Top Dead Centre) position for that piston. On many applications, this is done with a sensor that is mounted close to the harmonic balancer (aka crankshaft pulley), that is fitted with a reluctor ring whose teeth interrupt and complete a magnetic field by turns as the ring rotates with the crank shaft, thus creating the signal.

However, many applications also use sensors on the camshaft(s), injection pump, or flywheel/flex plate to either accomplish the same task, or to serve as a means to monitor the functioning of the crank shaft-mounted sensor. In addition, position sensors that are mounted on camshafts also serve to monitor and control variable valve/cam shaft timing. Regardless of the sensor type or other design specifics, as soon as the PCM fails to detect a signal from the engine position sensor, it will set code P0379, and may also illuminate a warning light.

The image below shows a typical engine position sensor, which in this case, is a Crankshaft Position Sensor. Note that while crankshaft position sensors often appear identical, all such sensors are unique to their application, and are therefore generally not interchangeable.

crank_sensor_large

What are the common causes of code P0379 ?

Some common causes of code P0379 could include the following-

  • Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors
  • Defective engine position sensors
  • Damaged, or clogged reluctor wheels
  • Excessive air gap between the reluctor wheel and sensor
  • Failed or failing PCM. Note that this is a rare event, and the fault must be sought elsewhere before any controller is replaced

What are the symptoms of code P0379 ?

Some common symptoms of code P0397 could include the following-

  • Stored trouble code and an illuminated warning light
  • In some cases, a hard starting condition may be present
  • In some cases, there may be misfires present throughout the engine’s operating range. In these cases, there will be one or more misfire related codes present
  • In many, if not most cases, a no-start condition will be present

How do you troubleshoot code P0379 ?

SPECIAL NOTES: Depending on the application, engine position sensors can be either of the three-wire Hall Effect type, or of the two-wire permanent magnet type. Both types are briefly described below-

Hall Effect sensors:

Sensors of this type always have three wires; one is a ground, one carries the sensors’ power supply (aka the reference voltage which is usually 5 volts), from the PCM to the sensor, while the third wire carries the signal generated by the sensor back to the PCM. In Hall Effect sensors, the reference voltage energizes an electromagnet whose field is interrupted as the teeth of the reluctor wheel passes in front of the electromagnet. The PCM counts the number of interruptions, and interprets the number of resulting pulses as the engine speed.

Permanent magnet sensors:

Sensors of this type always have two wires, and generate AC voltage signals as the teeth of the reluctor wheel passes in front of the magnet. The AC signal voltage is converted into a DC voltage by the analogue-to-digital signal converter that is built into the PCM. AS with Hall Effect sensors, the PCM counts the number of pulses, and interprets this as the engine speed.

It should also be noted that the operation of both types of sensor can be affected by problems and issues that are common to both, and while actual testing procedures vary between applications, some generic diagnostic/repair steps are common to both types of sensors. Refer to the trouble shooting steps below for more information. END OF SPECIAL NOTES.

Step 1

Record all codes present, as well as all available freeze frame data. This information can be of use should an intermittent fault be diagnosed later on.

Step 2

Refer to the manual to identify and locate all engine position sensors, as well as all associated wiring. Determine the exact routing, function, and color-coding of all relevant wiring to ensure that the correct circuits are tested later on.

 

NOTE: Refer to the manual to determine the exact relationship between all engine position sensors, as well as which sensor and its control circuit is most likely to produce code P0379 in addition to determining which part of the circuit is labelled “B”. Manufacturers do not always follow convention when it comes to labelling parts, components, and circuits, so make absolutely that the correct circuit is identified to avoid a misdiagnosis.

Step 3

One the correct sensor and circuit is identified, perform a thorough visual inspection of all wiring and connectors associated with that sensor. Look for damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors. Make repairs or replace wiring as required before clearing al codes and rescanning the system to see if the code returns.

 

NOTE: In most cases where damage to wiring is found, and especially on wiring between the sensor and the connector where the sensor connects with the main wiring harness, the best option is to replace the sensor with its wiring, as opposed to attempting repairs to wiring.

Step 4

If no visible damage to wiring is found, refer to the manual to determine the recommended air gap between the tip of the sensor and the reluctor wheel. Both permanent magnet and Hall Effect sensors can be affected by an excessive air gap, or by dirt, mud, and other foreign matter that clogs up the gaps between teeth on a reluctor wheel.

Reset the air gap as required (or where this is possible) and remove all foreign matter from the reluctor wheel. Also, check the reluctor wheel for any damage such as deformed teeth or cracks, both of which can seriously affect the operation of a sensor. Make repairs or replace the reluctor wheel as required, required before clearing al codes and rescanning the system to see if the code returns.

 

Step 5

If the code persists despite there being no visible damage to wiring, connectors, and sensors, prepare to perform resistance, continuity, ground, and if applicable, reference voltage tests  on all relevant wiring, but be sure to disconnect the wiring from the PCM to avoid damaging the controller during this step.

In the case of Hall Effect sensors, pay particular attention to the reference voltage and signal wires. Test the reference voltage circuit at the sensor connector; the reading should be 5 volts, or very close to 5 volt. If the reading is significantly lower, or if there is no current, refer to the manual for the correct procedure to follow to check if the PCM is actually delivering the correct reference voltage current. If it is not, replace the PCM.

However, if the PCM does deliver the correct current, check the resistance and continuity of the reference voltage wire, and make repairs or replace the wire to ensure that the full reference voltage reaches the sensor. Also, check the resistance of the signal wire between the sensor and the PCM. Compare this value with the value stated in the manual, and make repairs or replace the wire if a deviation is found.

In the case of permanent magnet sensors, perform resistance and continuity checks on the wiring between the sensor and the PCM, and repair or replace wiring as required if deviations from staed values are found.

Step 6

If the fault persists but all electrical values agree with stated values, prepare to test the sensor itself.

Hall Effect sensors:

Set the digital multimeter to DC Volts, and connect the red lead to the signal wire through the back of the connector, and the black lead to a suitable ground. Have an assistant crank the engine in one second “bursts” (do NOT allow the engine to start), and check the reading. If the sensor is producing a signal, the reading will fluctuate between full reference voltage and 0.  If no signal is produced, which is very likely, the sensor is defective and it must be replaced with an OEM part to ensure proper operation.

Permanent magnet sensors:

Start by testing the internal resistance of the sensor. Disconnect the sensor from the main harness, set the multimeter to Ohms (indicates resistance) and place a probe on each terminal in the connector- note that it does not matter which probe goes onto which terminal. In most cases, the reading will be somewhere between 500 ohm, and about 1 200 ohm; compare this reading with the recommended value stated in the manual, and replace the sensor if the obtained reading differs from the stated value by more than the maximum allowable amount.

If the sensors’ resistance checks out, reconnect the connector, set the multimeter to AC volts, and connect the red probe to the signal wire through the back of the connector. Connect the black lead to a suitable ground. Have an assistant crank the engine in short bursts while checking the reading. If the sensor produces a signal, the reading will fluctuate; if it does not, the sensor is defective and it must be replaced with an OEM part to ensure proper operation.

Step 7

The above steps will resolve code P0379 in nine out of every ten instances. However, in the unlikely event that the code persists beyond Step 6, it is almost certain that the issue is caused by an intermittent fault. Be aware though, that faults of this type can be extremely challenging and time consuming to find and repair. Therefore, if an intermittent fault is suspected, the better option would be to refer the application to the dealer or other competent repair facility for professional diagnosis and repair, since in some cases, this code can only be diagnosed accurately with the aid of an oscilloscope and a wave form library.

Codes Related to P0379

  • P0375 – Relates to “Timing Reference High Resolution Signal B Malfunction”
  • P0376 – Relates to “Timing Reference High Resolution Signal B Too Many Pulses”
  • P0377 – Relates to “Timing Reference High Resolution Signal B Too Few Pulses”
  • P0378 – Relates to “Timing Reference High Resolution Signal B Intermittent/Erratic Pulses”

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