P0379 Timing Reference High Resolution Signal "B" No Pulses

The P0379 diagnostic trouble code means that the engine control module (ECM/PCM) is not detecting the expected pulses from the Timing Reference High Resolution Signal “B” circuit.

This is a timing-related signal used by the engine management system to determine precise engine position and rotational timing. The word “No Pulses” is particularly important: the control module is expecting a repetitive high-resolution timing signal, but at some point it detects that the signal is missing completely.

P0379 does not automatically mean that a specific timing sensor has failed. The missing pulses can be caused by the sensor itself, its wiring, connector, power or ground supply, the timing/reluctor mechanism that generates the signal, or, in some cases, a problem elsewhere in the engine's synchronization system.

What Does “Timing Reference High Resolution Signal B” Mean?

Modern engines need much more precise position information than simply knowing whether the crankshaft is turning.

The ECM uses timing reference signals to determine things such as:

• Crankshaft position

• Engine speed

• Precise piston position

• Fuel injection timing

• Ignition timing

• Camshaft synchronization

• Variable valve timing operation

• Misfire detection

A high-resolution timing signal provides many pulses during each engine revolution. Because there are numerous pulses, the ECM can determine crankshaft movement very precisely.

The letter “B” identifies a particular timing-reference signal or circuit. Its exact physical source varies between manufacturers and engine designs. Therefore, P0379 should not automatically be interpreted as meaning “crankshaft position sensor B” on every vehicle.

What Does “No Pulses” Mean?

The phrase “No Pulses” describes what the ECM sees electrically.

The engine control module expects to see a rapidly repeating signal while the engine is rotating. If those pulses disappear, the ECM may set P0379.

This can happen in several ways:

• The sensor stops producing a signal.

• The signal wire is open.

• The sensor loses its power supply.

• The sensor loses its ground.

• A signal wire is shorted.

• The connector has poor contact.

• The reluctor or trigger wheel is damaged.

• The sensor is incorrectly positioned.

• Excessive sensor-to-target clearance prevents a usable signal.

• Mechanical timing has a problem.

• Electrical interference corrupts the signal.

• A timing component moves or becomes damaged.

• A control module or signal-processing problem exists.

Therefore, “no pulses” does not necessarily mean the engine has no mechanical timing signal at all. It means the ECM is not receiving the expected pulse pattern through the monitored circuit.

Where Does the Timing Signal Come From?

The exact design depends on the engine.

A timing reference may be generated using a:

• Hall-effect sensor

• Magnetic/variable-reluctance sensor

• Optical sensor

• Dedicated timing pickup

• Crankshaft reluctor wheel

• Camshaft trigger mechanism

• Other manufacturer-specific timing reference system

Some engines use multiple timing signals. Others integrate several functions into a smaller number of sensors and circuits.

This is why the manufacturer's wiring diagram and service information are important when diagnosing P0379. The terminology used by the scan tool does not always tell you the exact physical component without manufacturer-specific information.

Common Symptoms of P0379

The symptoms can range from a check-engine light with almost no noticeable drivability problem to a complete no-start condition.

Possible symptoms include:

• Check Engine Light

• Difficult starting

• Extended cranking

• Intermittent no-start

• Engine stalling

• Rough running

• Hesitation

• Poor acceleration

• Reduced engine power

• Unstable RPM signal

• Misfires

• Poor fuel economy

• Incorrect ignition timing

• Incorrect fuel injection timing

• Variable valve timing problems

• Limp-home operation

In some vehicles, the engine may continue running if another position signal is available. In other vehicles, losing a critical timing reference can prevent the ECM from correctly synchronizing fuel injection or ignition, resulting in a no-start.

Can P0379 Cause a No-Start?

Yes.

If the missing high-resolution timing signal is essential to the engine's synchronization strategy, the ECM may not know precisely where the crankshaft is during cranking.

The engine may crank normally with the starter but fail to start because the control module cannot establish the timing information required for ignition or injection.

However, not every vehicle will behave this way. Some systems have redundant timing information and can continue operating using another sensor or lower-resolution signal.

Common Causes of P0379

Faulty timing reference sensor

The sensor may fail internally and stop producing pulses, particularly when hot or under vibration.

Damaged wiring

A broken wire, internally fractured conductor, corrosion, or excessive resistance can interrupt the timing signal.

Poor connector contact

Loose terminals, corrosion, water intrusion, or damaged connector pins can cause the signal to disappear.

Loss of sensor power or ground

Some sensors require a dedicated power supply and ground. If either is missing, the sensor may produce no usable signal.

Short circuit

A signal wire may be shorted to ground, another circuit, or a power supply.

Damaged reluctor or trigger wheel

The sensor needs a properly shaped trigger target to generate its pulse pattern. Missing, damaged, bent, loose, or contaminated trigger components can interfere with signal generation.

Incorrect sensor installation

A sensor installed incorrectly or with excessive clearance from the trigger wheel may fail to produce a reliable signal.

Mechanical timing problems

A stretched or damaged timing chain, incorrect timing, damaged sprocket, or other mechanical problem can alter the relationship between timing components.

Electrical interference

Ignition systems, alternators, poorly routed wiring, or other electrical sources can sometimes interfere with sensitive timing signals.

Control module problem

An ECM/PCM problem is possible, but it should normally be considered only after the sensor, wiring, power, ground, signal generation, and mechanical timing have been properly tested.

P0379 Is Not the Same as a Generic Sensor Failure

This distinction is important when diagnosing the code.

A technician should not simply see P0379 and replace a timing sensor.

For example, imagine a sensor that normally produces a pulse signal while the engine is running. If the sensor connector has a broken terminal, the sensor itself may be perfectly functional. The ECM will still see no pulses and can set P0379.

Likewise, a damaged reluctor can produce the same diagnostic result even when the sensor and wiring are good.

The DTC tells you what the ECM is not seeing. It does not necessarily identify the component responsible for that condition.

How P0379 Should Be Diagnosed

A systematic diagnosis is much more effective than replacing parts based solely on the code.

1. Scan all modules

First check for other stored, pending, or manufacturer-specific DTCs.

Codes relating to crankshaft position, camshaft position, synchronization, ignition, fuel injection, or communication can provide important clues.

2. Check the freeze-frame data

Look at the conditions under which P0379 was recorded.

Pay attention to:

• Engine RPM

• Engine temperature

• Vehicle speed

• Battery voltage

• Engine load

• Starting versus running condition

If the code repeatedly appears during cranking, the diagnosis should focus heavily on whether the timing signal is actually being generated while the engine is turning.

3. Identify the exact “B” circuit

Do not assume that “B” means the same component on every vehicle.

Use the manufacturer's service information to determine:

• Which sensor or timing circuit is Signal B

• Sensor type

• Pin configuration

• Power supply

• Ground

• Signal wire

• Trigger source

• Expected waveform

4. Inspect the sensor and connector

Look for:

• Broken connector locks

• Bent pins

• Corrosion

• Oil contamination

• Water intrusion

• Loose terminals

• Damaged insulation

• Harness rubbing

• Wiring stretched near the sensor

A visual inspection can sometimes reveal the cause before electrical testing begins.

5. Check power and ground

If the sensor requires an external power supply, verify that it is actually present under the conditions specified by the manufacturer.

Do not rely solely on a voltage reading with the circuit unloaded. A poor connection can show normal voltage with almost no current flowing and fail when the circuit is operating.

Voltage-drop testing can be useful for identifying poor power or ground connections.

6. Verify the signal

This is one of the most important steps with P0379.

A scan tool may show an engine RPM value, but RPM alone does not always prove that the high-resolution Signal B waveform is correct.

Where appropriate, an oscilloscope can show:

• Presence of pulses

• Signal amplitude

• Frequency

• Missing pulses

• Irregular pulses

• Electrical noise

• Distorted waveform

• Changes during cranking and acceleration

The expected waveform depends entirely on the sensor and engine design.

7. Check the trigger mechanism

If the sensor and wiring are electrically sound but the pulse signal is missing, inspect the component that generates the signal.

Depending on the engine, this may include:

• Reluctor wheel

• Trigger wheel

• Tone wheel

• Camshaft target

• Crankshaft target

• Timing gear

• Timing chain components

A damaged or loose trigger can cause the sensor to appear defective even when the sensor itself is working.

8. Check mechanical timing

If the electronic signal appears abnormal or synchronization data is inconsistent, mechanical timing should be investigated.

Possible problems include:

• Stretched timing chain

• Incorrect timing after repair

• Damaged timing sprocket

• Broken timing component

• Incorrect cam/crank relationship

• Variable valve timing problems

P0379 and the Crankshaft/Camshaft Relationship

The ECM does not evaluate timing signals in isolation.

It may compare different position signals to determine whether the crankshaft and camshaft are synchronized.

If one signal disappears, becomes distorted, or arrives at an unexpected time, the ECM may detect a synchronization problem.

This means P0379 can sometimes appear alongside camshaft or crankshaft position codes.

If several timing-related DTCs appear together, replacing one sensor immediately may not solve the problem. The underlying issue could be wiring, a shared power/ground circuit, a damaged trigger mechanism, or mechanical timing.

Hall-Effect and Magnetic Sensors Require Different Tests

Not every timing sensor works in the same way.

A Hall-effect sensor generally requires an electrical supply and produces a digital-style switching signal.

A variable-reluctance sensor generates its own alternating signal as the target passes the sensor, with the characteristics changing according to engine speed.

Because of these differences, there is no single universal voltage or resistance value that can be used to diagnose every P0379 vehicle.

Testing should follow the specifications for the particular engine.

Could Low Battery Voltage Cause P0379?

It can contribute to timing-related faults in some vehicles.

During cranking, a weak battery can cause system voltage to fall significantly. If the timing sensor, ECM, or associated electronics cannot operate correctly at the available voltage, the expected signal may not be generated or recognized.

However, low battery voltage should not automatically be blamed for P0379.

Check the battery, starter current draw, cranking voltage, and charging system when the symptoms suggest a voltage problem.

Can P0379 Be Caused by a Timing Chain Problem?

Yes, depending on the engine's timing-reference design.

A mechanical timing problem can change the relationship between the trigger mechanism and the sensor. In severe cases, a damaged or displaced timing component can prevent the expected pulse pattern from being generated.

If P0379 appears together with:

• Cam/crank correlation codes

• Abnormal engine noise

• Difficult starting

• Sudden stalling

• Backfiring

• Loss of compression

• Multiple synchronization codes

then mechanical timing should be considered carefully.

P0379 vs Other Timing Reference Codes

P0379 specifically indicates no pulses from the monitored Timing Reference High Resolution Signal “B”.

Other timing reference codes can describe different conditions, such as:

• P0376 – Timing Reference High Resolution Signal “B” Too Many Pulses

• P0377 – Timing Reference High Resolution Signal “B” Too Few Pulses

• P0378 – Timing Reference High Resolution Signal “B” Intermittent/Erratic Pulses

• P0379 – Timing Reference High Resolution Signal “B” No Pulses

The distinction is useful because P0379 indicates a complete absence of the expected pulse signal, whereas P0378, for example, indicates an unstable or intermittent signal.

Is It Safe to Drive With P0379?

If the vehicle starts and runs normally, it may be possible to drive a short distance for diagnosis.

However, caution is appropriate because a timing-reference signal can be critical to engine operation.

Do not continue driving if you experience:

• Engine stalling

• Repeated no-start conditions

• Severe misfire

• Major loss of power

• Sudden hesitation

• Abnormal engine operation

An engine that loses an essential timing signal while driving can stall unexpectedly.

If P0379 is accompanied by significant timing-chain noise or suspected mechanical timing failure, continued operation can potentially make the underlying problem worse.

A Practical Diagnostic Order

A good diagnostic approach for P0379 is:

P0379 → scan all codes → check freeze-frame → identify Signal B → inspect sensor and connector → check wiring → verify power and ground → check the actual signal → inspect trigger mechanism → compare synchronization signals → check mechanical timing → repair → clear codes → road test and verify.

This approach prevents unnecessary replacement of sensors, wiring, or the ECM.

Final Perspective

P0379 – Timing Reference High Resolution Signal “B” No Pulses means the ECM is not detecting the expected high-resolution timing pulses from the monitored Signal B circuit.

The fault may be electrical, electronic, or mechanical. A failed sensor is certainly possible, but so are a damaged connector, broken wire, missing power or ground, short circuit, incorrect sensor installation, damaged reluctor, or a mechanical timing problem.

Because these signals can be fundamental to engine synchronization, P0379 deserves proper diagnosis rather than simply clearing the code or replacing a sensor. The most useful evidence comes from identifying exactly what Signal B represents on the vehicle, checking the circuit, and—when necessary—observing the actual timing waveform while the engine is cranking and running.