P0374 Timing Reference High Resolution Signal "A" No Pulses

P0374 means the engine control module has detected that the high-resolution Timing Reference Signal “A” is not producing the expected pulses.

This is an important distinction because the code does not simply mean “the crankshaft sensor is bad.” The exact component represented by Signal “A” depends on the manufacturer and engine management system. On some vehicles it may be closely related to the crankshaft position/timing system, while on others it can refer to a dedicated high-resolution timing signal generated by a particular sensor or timing reference circuit.

The ECM relies on this signal to know exactly where the engine is in its rotational cycle. If the expected pulses disappear, the module may lose accurate information about crankshaft position and engine speed.

What Does “High Resolution Timing Reference” Mean?

A normal engine position signal gives the ECU information about crankshaft or camshaft movement. A high-resolution timing reference signal provides much more detailed timing information by generating a large number of pulses during engine rotation.

These pulses allow the ECM to determine very precise crankshaft position.

The information can be used for:

• Fuel injection timing

• Ignition timing

• Engine synchronization

• Misfire detection

• Variable valve timing control

• Precise RPM calculation

• Crankshaft position tracking

• Injection synchronization on diesel engines

Because the signal contains many timing events, even a relatively short interruption can become important to the engine controller.

What Does “No Pulses” Actually Mean?

The important part of P0374 is “No Pulses.”

The ECM is expecting to see a repeating electrical waveform from Signal A, but during the monitored operating conditions it sees no valid timing pulses.

This can happen because:

• The sensor has stopped producing a signal.

• The signal wire is open.

• The signal is shorted to ground.

• Sensor power or ground is missing.

• A connector has lost contact.

• The trigger/reluctor wheel is damaged.

• The sensor has excessive clearance from the trigger target.

• The wrong sensor has been installed.

• Electrical interference is preventing the ECM from recognizing the signal.

• A mechanical timing problem prevents the target from passing the sensor correctly.

• The ECM cannot correctly process the signal.

Therefore, P0374 is fundamentally a timing signal availability problem, not automatically a sensor replacement code.

Common Symptoms of P0374

The symptoms depend heavily on how the vehicle uses Signal A.

A vehicle may experience:

• Check Engine Light

• Hard starting

• Extended cranking

• No-start condition

• Engine stalling

• Sudden loss of power

• Hesitation during acceleration

• Rough running

• Misfires

• Unstable or incorrect RPM reading

• Reduced engine performance

• Poor fuel injection timing

• Transmission shift problems on some vehicles

In some applications, the engine may continue running because another position signal is available as a backup. In other applications, losing the high-resolution timing signal can prevent the engine from starting or cause it to shut down.

What Can Cause P0374?

Faulty timing reference sensor

The sensor may work intermittently at first and then completely lose its output. Heat can be particularly important with electronic sensors; a sensor may produce a normal signal when cold and stop producing pulses after reaching operating temperature.

Open or damaged wiring

A broken signal wire can completely interrupt communication between the sensor and ECM.

This is particularly common where the harness passes close to:

• The engine

• Exhaust components

• Moving parts

• Sharp brackets

• High-temperature areas

Short to ground or voltage

A damaged signal wire touching another circuit can prevent the ECM from recognizing the timing pulses.

Poor connector connection

Loose terminals, corrosion, water intrusion or damaged connector pins can interrupt the signal.

An apparently clean connector can still have a terminal that has lost its proper tension.

Missing sensor power or ground

For an active Hall-effect or similar sensor, the sensor may require a dedicated supply and ground. If either is missing, the output signal can disappear completely.

Damaged reluctor or trigger wheel

The sensor itself may be perfectly functional, but the target it is supposed to detect may be damaged, contaminated, incorrectly positioned or physically damaged.

Incorrect sensor installation

An excessive sensor-to-target air gap can reduce or eliminate the signal. An incorrectly installed or incorrect replacement sensor can produce the same type of problem.

Mechanical timing problem

A damaged timing component or abnormal movement of the timing target can affect the reference signal.

However, P0374 by itself does not prove that the timing chain or timing belt has failed. Mechanical timing should be investigated when waveform or synchronization evidence points in that direction.

ECM problem

An ECM input circuit or internal processing problem is possible, but it should normally be considered only after the sensor, wiring, power, ground and trigger target have been verified.

How P0374 Should Be Diagnosed

The first step should not be replacing the sensor.

A technician should begin by scanning all stored and pending codes and examining freeze-frame information. Other crankshaft, camshaft, synchronization or communication codes can provide important clues.

Next, the technician needs to determine exactly what Timing Reference Signal “A” represents on that particular engine. This requires the manufacturer's wiring diagram and service information because the generic OBD-II description does not identify the physical component universally.

Then the circuit should be inspected.

Look for:

• Damaged insulation

• Broken wires

• Oil contamination

• Corrosion

• Loose terminals

• Water intrusion

• Incorrect routing

• Harness contact with hot components

• Connector damage

A simple continuity test is not always enough. A wire can show continuity with the circuit inactive but develop excessive resistance or lose connection when the engine vibrates.

A wiggle test can therefore be very useful when the problem is intermittent.

Check Power, Ground and Signal

If the sensor requires an external power supply, verify that the correct voltage reaches the sensor.

The ground should also be tested under realistic operating conditions rather than simply assuming that a ground wire is good because it shows continuity.

The signal circuit then needs to be examined.

This is where an oscilloscope can provide much more information than a basic multimeter.

A healthy high-resolution timing signal should produce a consistent repeating waveform appropriate to the particular sensor and engine.

With P0374, the critical question is:

Is the sensor actually producing pulses, and does the ECM receive those pulses?

If the signal exists at the sensor but disappears before reaching the ECM, the wiring becomes the primary suspect.

If there is no signal directly at the sensor, the technician must investigate the sensor, its power/ground, air gap and trigger target.

Oscilloscope Testing Is Especially Valuable

P0374 is one of those codes where oscilloscope testing can be extremely informative.

A scope can show whether the signal:

• Exists

• Completely disappears

• Drops out intermittently

• Has an abnormal amplitude

• Contains electrical noise

• Has distorted pulses

• Changes with engine speed

• Disappears only when the engine becomes hot

• Is synchronized correctly with another timing signal

If the signal disappears at the sensor itself, replacing wiring downstream will not solve the problem.

If the waveform is healthy at the sensor but absent at the ECM connector, the problem is almost certainly between those two points.

This allows the repair to be based on evidence rather than guesswork.

Do Not Automatically Blame the Crankshaft Sensor

Because P0374 concerns timing reference information, it is easy to assume that the crankshaft position sensor must be defective.

That conclusion can be wrong.

Depending on the vehicle, the problem could instead involve:

• Another timing sensor

• Sensor power

• Sensor ground

• Signal wiring

• Connector terminals

• Trigger wheel

• Sensor installation

• Mechanical timing

• ECM input circuitry

The exact definition of Signal A is manufacturer-specific, so the vehicle's wiring diagram and service information should always be consulted before identifying the part.

Mechanical Timing Should Be Checked When Necessary

If the electrical circuit and sensor waveform are correct but the timing information is still missing or inconsistent, the mechanical side should be investigated.

Possible issues include:

• Damaged reluctor teeth

• Loose trigger wheel

• Damaged timing gear

• Excessive timing-chain movement

• Incorrect timing-chain installation

• Damaged timing belt components

• Abnormal camshaft/crankshaft relationship

Again, this should be confirmed with testing.

A technician should not replace a timing chain simply because P0374 is present.

P0374 vs Other Timing Reference Codes

P0374 specifically indicates no pulses from Timing Reference Signal A.

That makes it different from codes where pulses are present but their number, timing or quality is incorrect.

For example:

• P0374 – Signal A has no detected pulses.

• P0373 – Signal A is intermittent.

• P0372 – Signal A has too few pulses.

• P0371 – Signal A has too many pulses.

• P0370 – Timing Reference Signal A circuit malfunction.

The distinction is useful during diagnosis. A “no pulses” code directs attention toward a complete loss of signal, whereas a pulse-count or intermittent code suggests that the signal exists but is incorrect or unstable.

Can P0374 Cause a No-Start?

Yes.

If the affected timing reference signal is essential for engine synchronization, the ECM may be unable to determine the correct position of the crankshaft or coordinate fuel and ignition events.

In that situation, the engine may crank normally but fail to start.

However, whether P0374 causes a complete no-start depends on the vehicle's specific engine-management strategy. Some systems can use another position signal as a backup.

The Correct Repair Depends on Where the Signal Is Lost

There is no single repair for P0374.

The final repair might involve:

• Replacing a defective timing reference sensor

• Repairing an open signal wire

• Repairing a shorted circuit

• Replacing damaged connector terminals

• Restoring sensor power or ground

• Correcting sensor installation or air gap

• Repairing a damaged reluctor/trigger wheel

• Correcting a mechanical timing problem

• Repairing an ECM circuit in rare cases

The important point is that the component should be replaced only after the signal path has been tested.

Final Diagnostic Summary

P0374 – Timing Reference High Resolution Signal “A” No Pulses means the ECM expected to see high-resolution timing pulses from Signal A but detected none during the relevant operating conditions.

The most important diagnostic question is not simply “Is the sensor bad?” but:

“Where is the timing signal being lost?”

Start by identifying exactly what Signal A represents on the specific vehicle. Then verify sensor power and ground where applicable, inspect the wiring and connectors, examine the signal with an oscilloscope, and check the trigger target. Only after the electrical signal path has been proven should mechanical timing or ECM faults become the main focus.

A P0374 diagnosis based solely on replacing the timing sensor can easily miss a broken wire, poor connector terminal, missing ground, damaged trigger wheel or another problem that is preventing the ECM from seeing the pulses.