P0373

Timing Reference High Resolution Signal A Intermittent/Erratic Pulses

P0373 is a generic OBD-II powertrain diagnostic trouble code: Timing Reference High Resolution Signal A Intermittent/Erratic Pulses. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0373
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
Need P0373 disabled?
RaceTune permanently disables any OBD-II trouble code on supported ECUs — for motorsport, off-road, and export use.
→

What P0373 means

P0373 — "Timing Reference High Resolution Signal 'A' Intermittent/Erratic Pulses" — is set when the PCM detects that the high-resolution engine position pulse train is present but irregular: pulses arrive at inconsistent intervals, drop out momentarily, or vary in amplitude in a way that prevents reliable crank/cam position tracking. The high-resolution signal provides the PCM with precise, cycle-by-cycle timing data used for ignition advance calculation, direct injection phasing, and variable cam phaser feedback. When this signal becomes erratic, timing events can occur out of sequence, causing rough combustion.

P0373 belongs to the same family as P0372 (too few pulses) and P0374 (no pulses) but distinguishes itself by the intermittent nature of the fault — the signal returns to normal between dropout events, making it challenging to isolate under static workshop conditions. The erratic pattern is most commonly caused by a loose or corroded connector that makes and breaks contact under vibration, a cracked wiring harness that flexes open under heat or mechanical stress, electromagnetic interference from a nearby component, or a reluctor ring with a damaged tooth that causes one irregular pulse per revolution. Oscilloscope analysis is the definitive diagnostic tool, as it captures the irregular pulse spacing that a standard scan tool PID cannot resolve.

Driveability effects are typically intermittent: rough idle that comes and goes, hesitation or stumble during acceleration, occasional misfires, and in some cases temporary stalling. The PCM may not enter limp mode immediately because the signal recovers, but extended periods of erratic input can cause persistent misfire logging or adaptive timing corrections that degrade performance.

Common causes

Most-frequently reported root causes when P0373 is logged.

  • 1
    Loose, corroded, or intermittently contacting connector pin at the crankshaft or camshaft position sensor.
  • 2
    Chafed or pinched signal wiring that opens and closes intermittently under vibration or thermal cycling.
  • 3
    Single damaged or cracked tooth on the reluctor ring creating one irregular pulse per revolution.
  • 4
    Electromagnetic interference (EMI) from a failing alternator, ignition component, or aftermarket accessory inducing noise onto the signal line.
  • 5
    Moisture or condensation ingress into the sensor connector causing intermittent short circuits.
  • 6
    Sensor internal degradation — partially failed Hall-effect element producing inconsistent output under certain operating conditions.
  • 7
    Weak or fluctuating 5V reference voltage causing unstable signal thresholds.
  • 8
    PCM input circuit intermittent solder joint or pin corrosion.

Symptoms drivers notice

MIL / Check Engine Light illuminates, often with intermittent pending codes.
Rough idle that fluctuates — engine may smooth out temporarily then roughen again.
Hesitation or stumble during light-throttle acceleration.
Occasional misfires across one or more cylinders.
Temporary power loss or stalling, especially at low RPMs or during deceleration.
Intermittent erratic tachometer readings during fault events.
Possible limp mode or torque reduction on platforms with strict timing validation if the fault frequency is high.

How to diagnose P0373

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and retrieve all stored codes, noting concurrent misfire codes or P0372/P0374 that suggest the fault is progressing.
  2. 2
    Wiggle test the sensor connector and wiring harness while monitoring the live engine speed (RPM) PID — a dropout or spike during connector movement confirms an intermittent connection.
  3. 3
    Inspect the sensor connector for corrosion, spread pins, and moisture; clean or replace the connector if contamination is found.
  4. 4
    Visually examine the wiring harness along its full length for chafing, pinch points near brackets, and heat damage.
  5. 5
    Measure 5V reference voltage, ground continuity, and signal circuit continuity at the connector with a digital multimeter.
  6. 6
    Use an oscilloscope on the signal wire during a road test to capture the pulse waveform — erratic pulses show as uneven spacing, amplitude variation, or partial dropouts in the otherwise regular square wave.
  7. 7
    Inspect the reluctor ring for a single cracked or damaged tooth that would produce one anomalous pulse per engine revolution.
  8. 8
    Replace the sensor after confirming wiring and connector integrity; retest with an extended drive cycle under conditions that previously triggered the fault.

Related powertrain codes

Frequently asked questions

Why is P0373 harder to diagnose than P0372 or P0374?

P0373 is intermittent by definition — the signal recovers between fault events, so the fault may not be present during a static workshop inspection. Standard scan tool PIDs sample at low frequency and can miss brief dropouts. An oscilloscope captures every pulse in real time, making it the essential tool for catching the erratic pattern that defines P0373.

Can a bad alternator cause P0373?

Yes. A failing alternator can produce high levels of AC ripple or voltage spikes on the electrical system that couple onto the sensor signal line, creating electrical noise the PCM interprets as erratic pulses. Checking alternator output AC ripple (should be below 0.5V AC) is a worthwhile step when wiring and sensors appear intact.

Is P0373 serious enough to stop driving?

Short-term driving is generally possible, but an erratic timing reference risks stalling at inopportune moments and can cause the PCM to log false misfires. The condition typically worsens with time and heat cycling, so prompt diagnosis is advised before it progresses to a complete signal loss (P0374).

What is the relationship between P0373 and misfires?

An erratic high-resolution timing signal causes imprecise ignition and injection timing, which can directly cause misfires. Additionally, some PCMs use the timing reference to validate the misfire monitor itself; an erratic signal may suppress genuine misfire detection or generate false misfire codes as a secondary effect.

Disabling P0373 in software

RaceTune can permanently disable P0373 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

Got P0373 in your scan?

Upload your ECU file — we'll identify the exact software version and confirm whether a disable is available for your car.

Upload your file