OBD-II trouble code
P0373: Timing Reference High Resolution Signal 'A' Intermittent/Erratic Pulses
The fault that is never there when you look. This code is diagnosed by capturing an event, not by testing a component — and the freeze frame is worth more than an hour under the bonnet.
Quick facts
- System
- Powertrain
- Category
- Sensors / Timing
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $120 – $900
- DIY difficulty
- Advanced DIY
What does P0373 mean?
Of everything in this family, P0373 is the only member that describes a fault which is usually absent by the time anyone goes looking for it. The pulse train is not consistently wrong. It is right, then briefly wrong, then right again — edges arriving where no edge should be, edges skipped, timing that jitters for a fraction of a second. The module cannot make sense of it, records the event and moves on, and by the time the car is on a ramp everything measures perfectly.
That changes what diagnosis even means here. Component testing answers the question 'is this part good right now', which is the wrong question. The right question is 'what were the conditions when it went wrong', and the freeze frame data captured with the code is the only witness. Coolant temperature at the moment of the fault is the single most valuable field in it. A code set at full operating temperature after twenty minutes of running points at something that expands when hot — a hairline crack in a sensor's potting, a fractured winding that opens as it grows, a semiconductor drifting past its threshold. A code set within a minute of a cold start on a damp morning points somewhere else entirely: moisture bridging a connector, or a contact that has to warm up before it seats.
Engine speed and load in the freeze frame do similar work. Faults that appear only at higher revs or under load are usually vibration and movement — a harness that swings against a bracket, a terminal that loses contact when the engine rocks on its mounts, a chafe that only touches when the loom is pushed. Faults that appear at steady cruise with the engine settled are more often thermal.
There is a specific trap worth naming. Misfire detection works by measuring tiny differences in crankshaft speed between firing events, and it does that measurement on the high-resolution signal. When the signal jitters, the maths produces misfires that never happened. So a car with P0373 frequently arrives carrying random misfire codes as well, and the misfires are the effect rather than the cause. Chasing them means buying coils and injectors for an engine that is combusting perfectly.
The other thing to say plainly is that this is the code most often 'fixed' twice. A sensor gets fitted, the fault stays away for a fortnight because intermittents do that, and it returns. Confirming the fault while it is happening is slower than guessing and is the only approach that ends the job.
Common causes
- Hairline crack in the sensor body or potting that opens as the component reaches operating temperature
- Partially fractured winding or internal connection that separates under heat and reconnects when cool
- Spread or relaxed terminal in a connector making contact at rest and losing it under vibration
- Moisture or corrosion inside a connector that bridges intermittently and dries out at temperature
- Chafed wire touching a ground or an adjacent circuit only when the harness moves
- Loose sensor mounting bolt allowing the air gap to vary as the engine rocks under load
- Reference wheel with a loose or slightly out-of-round fit that wobbles at particular speeds
- Intermittent noise coupling from a failing shield ground that is otherwise still connected
Symptoms
- Check engine light that comes on and later goes out again on its own
- Sudden brief stumble, cut or lurch while driving that clears immediately
- Random or multiple-cylinder misfire codes with no actual combustion problem present
- Intermittent stalling with an immediate successful restart
- Occasional long crank or a no-start that resolves the next time the key is turned
- Tachometer flicker or a momentary drop in the reading while driving steadily
Diagnostic steps
- 1.Read and write down the freeze frame before clearing anything. Coolant temperature, engine speed, load and run time at the moment of the fault are the only direct evidence of the conditions that trigger it.
- 2.Use the coolant temperature reading to choose a direction. Fully warm points at thermal expansion inside the sensor or a connector; near-ambient on a damp day points at moisture and contact resistance.
- 3.Check whether misfire codes are also stored. If they are random, spread across cylinders and unaccompanied by any real running fault, treat them as a symptom of the jittery signal rather than as separate problems.
- 4.Set a scope to trigger on a missing or extra edge and leave it armed while you work. A meter cannot see an event that lasts milliseconds.
- 5.With the scope armed, wiggle-test the harness, the connector and the sensor body section by section. Reproducing the glitch by hand names the location precisely.
- 6.Apply freeze spray to the sensor body once it is fully warm, then heat it gently with a hot air gun, watching the waveform. A part that changes behaviour with temperature has just confessed.
- 7.Check terminal tension with a matching male pin rather than by eye. A terminal that has relaxed still looks perfect and still fails under vibration.
- 8.Inspect the connector for green corrosion, water staining and a failed seal. Dry it, treat it and monitor rather than assuming the sensor is at fault.
- 9.Verify the sensor mounting bolt torque and check for elongated mounting holes, which let the gap change as the engine moves on its mounts.
Repair cost
$120 – $900
Diagnosis is a larger share of the bill on this code than on any other in its family, because the work is capture rather than measurement. Expect $120 to $350 in diagnostic time, and be wary of anyone quoting a part before the fault has been observed. Connector repair, terminal replacement and reseating are $100 to $300. A replacement sensor is $40 to $200 in parts and $150 to $450 fitted. Harness repair where a chafe has to be found runs $150 to $500 because the searching is the job. Budget for the possibility of a second visit — intermittents that stay away for two weeks after a repair have not necessarily been fixed.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with crankshaft position sensor replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an advanced DIY job. It typically requires specialty tools, scan-tool access, lifting equipment, or careful sequencing to avoid causing new failures. Plan for extended downtime and have a backup vehicle. Most owners are better served by a shop that has done this repair before.