OBD-II trouble code
P0372: Timing Reference High Resolution Signal 'A' Too Few Pulses
Pulses are going missing from the fine timing reference. Unlike most sensor codes, the expensive answer here is the toothed wheel, not the sensor reading it.
Quick facts
- System
- Powertrain
- Category
- Sensors / Timing
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $150 – $2,500
- DIY difficulty
- Advanced DIY
What does P0372 mean?
P0372 sets when the module counts fewer high-resolution timing pulses per revolution than the engine should be producing. It is the mirror image of the too-many-pulses fault, and the difference in direction matters more than it sounds, because a subtractive fault has a completely different suspect list. Pulses go missing for two broad reasons: either the sensor is not being given enough magnetic change to detect, or the change is happening but the signal arriving at the module is too weak to be counted.
That first possibility is why this code deserves more attention on the reference wheel than any other member of its family. A high-resolution track exists precisely because it has many more teeth than the coarse one, and the price of packing more teeth into the same circumference is that each tooth is smaller and shallower. Small features are easier to damage, easier to clog and easier to lose. A single chipped, cracked or packed tooth removes exactly one pulse per revolution, which is enough to trip the count and nothing like enough to stop the engine — so the fault often presents as a code and a vague complaint rather than a breakdown.
Air gap is the second thing this code turns on, and it is routinely underestimated. A magnetic pickup's output depends on how much flux changes as a tooth passes, and a small tooth moves less flux than a large one. An air gap that is perfectly adequate for the coarse track can be marginal for the fine one, which means a sensor that is not fully seated, that has a smear of sealant or a stray washer behind its flange, or that is simply the wrong part number with a slightly shorter nose, can produce this code and only this code. Anyone who has just replaced a sensor and gone straight from one fault to this one should suspect the installation before suspecting the part.
There is a diagnostic consequence that belongs to this code alone. A variable-reluctance pickup generates more output as speed rises, so a marginal gap or a weakened magnet starves the signal at low speed first. If the count is short during cranking and at idle but cleans up as the engine revs, the fault is amplitude — gap, magnet, corrosion in the circuit. If instead the count stays short at every speed, or gets worse as revs climb, the fault is in the tooth pattern itself. That one question sorts a cheap repair from an expensive one before any part is ordered.
On engines that derive the high-resolution reference from the camshaft rather than the crankshaft, a stretched timing chain adds a third possibility. The pulses are all present but arriving progressively later relative to the crank, and some strategies score that as a shortfall against the window they were expected in.
Common causes
- Chipped, cracked or missing tooth on the fine-toothed high-resolution reference track
- Debris, casting flash or hardened oil sludge packed into the gaps between fine teeth
- Excessive air gap from a sensor that is not fully seated, has debris behind its flange, or is the wrong part number
- Weakened magnet in an aged variable-reluctance pickup producing too little output at low speed
- High resistance from corrosion in the signal circuit dropping pulse amplitude below the counting threshold
- Reference wheel that has shifted, loosened or been fitted out of position after engine work
- Stretched timing chain on engines that take the high-resolution reference from the camshaft
- Cracked or partially open winding inside the sensor dropping output as it warms
Symptoms
- Check engine light on with the engine otherwise running acceptably
- Extended cranking before the engine catches, especially when cold
- Rough or unstable idle that smooths out at higher engine speeds
- Hesitation, flat spots and reduced power under load
- Misfire readiness monitor unable to complete, causing an emissions test to be refused
- Occasional stalling at low speed or when coming to a stop
Diagnostic steps
- 1.Establish whether the shortfall is speed-dependent. Scope the signal while cranking, at idle and at a raised steady speed, and count pulses per revolution at each. A count that improves with speed is an amplitude problem; a count that stays short at every speed is a tooth problem.
- 2.Ask whether the sensor has been out recently. A sensor fitted with sealant, a spacer, debris behind the flange or simply not pushed fully home produces this code from an otherwise perfect installation.
- 3.Compare the part number on the fitted sensor against the correct one for the engine. A nose that is a millimetre short changes the air gap enough to matter on a fine-toothed track and not enough to matter on a coarse one.
- 4.Measure air gap directly where the design allows it, and compare it against specification rather than against what looks reasonable.
- 5.Measure pulse amplitude at the module end rather than at the sensor. The module counts what reaches it, so a healthy waveform at the sensor and a shrunken one at the module names the wiring as the fault.
- 6.Perform a voltage drop test on the signal and ground legs with the engine running. Corrosion inside a connector shows up as lost amplitude and is invisible to a continuity check.
- 7.Inspect the reference track itself with a borescope or by removing the sensor and rotating the engine slowly. One damaged tooth is all this code needs and it is easy to look past.
- 8.On camshaft-referenced systems, verify camshaft-to-crankshaft correlation before condemning the sensor. A stretched chain presents as a timing fault, not as a wiring fault.
Repair cost
$150 – $2,500
The spread here is unusually wide because the same code covers a twenty-minute fix and a gearbox-out job. Reseating a sensor correctly or repairing a corroded connector is $100 to $300. A replacement sensor is $40 to $200 in parts and $150 to $450 fitted. Cleaning packed debris from the reference track can be inexpensive if the wheel is accessible and expensive if it is not. A damaged reluctor ring is the case that hurts: pressed onto the crank snout it means front cover and possibly balancer removal at $600 to $1,400, and integral to the flywheel or flexplate it means the transmission comes out, commonly $1,200 to $2,500. A stretched timing chain on a camshaft-referenced engine is its own major job.
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.