OBD-II trouble code
P0323: Ignition/Distributor Engine Speed Input Circuit Intermittent
The signal drops out briefly and then comes back, so everything tests perfect in the workshop. Heat is the usual reason, and reproducing the fault deliberately is worth more than any measurement taken on a cold engine.
Quick facts
- System
- Powertrain
- Category
- Sensors / Timing
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $130 – $800
- DIY difficulty
- Advanced DIY
What does P0323 mean?
An intermittent fault is a different discipline from a permanent one. There is no measurement to take, because whatever is wrong is not wrong at the moment you are looking. The whole job becomes making the fault happen on demand, and until you can do that, every part you fit is a guess dressed up as a repair.
The dominant reason this particular signal comes and goes is temperature. Engine speed sensors sit against the block, near the exhaust or inside the bellhousing, and they reach temperatures that most electronics never see. A winding with a hairline break expands as it warms until the two ends separate; a semiconductor with a degraded junction stops switching cleanly once it is hot enough. Both produce the same signature, and it is one of the most recognisable patterns in diagnostics: the car starts and runs perfectly cold, dies after twenty or thirty minutes, refuses to restart, and then fires up without complaint after it has sat long enough to cool. If a customer describes that sequence, they have effectively finished the diagnosis for you.
That pattern also explains why 'I tested it and it was fine' is such a common dead end here. Resistance and voltage checks on a cold sensor tell you about a cold sensor. The correct test is to make it hot deliberately — a heat gun aimed at the sensor body while live engine speed is watched on a scan tool, with the reading dropping out as the temperature climbs — and then to cool it with a blast of freeze spray and watch it come back. That is a positive identification rather than an inference.
The second cause worth taking seriously is one that barely matters on the other codes in this family: electrical interference. A signal has to be badly degraded before it disappears altogether, but a marginal signal only needs a little noise on top to be corrupted occasionally. Aftermarket amplifiers and their power cables run alongside factory harnesses, ignition leads laid across a sensor wire couple high voltage into it every time a plug fires, and an alternator with one failed diode puts alternating ripple onto the whole vehicle's supply. Each of these produces a fault that follows the driver's behaviour rather than the engine's condition — worse with the stereo on, worse at certain engine speeds, worse once the battery has aged.
Mechanical intermittence is the third possibility. A cracked mounting boss, a bolt that has loosened, or a bracket fatigued at a spot weld will let the sensor move under vibration, so the air gap is correct at idle and wrong over a bump or at a particular resonant engine speed.
Because the evidence is fleeting, freeze frame data is worth more on this code than on almost any other. Coolant temperature, engine speed, load and vehicle speed captured at the instant the code set will usually tell you whether you are chasing heat, vibration or noise before you pick up a tool.
Common causes
- Sensor that fails only once it reaches operating temperature and recovers as it cools
- Hairline break in the sensor winding that opens as the wire expands with heat
- Corroded or slack connector pin that makes and breaks with vibration
- Wiring chafed against a bracket, so contact is only lost when the engine rocks under load
- High-tension lead or aftermarket power cable routed alongside the signal wire, coupling noise into it
- Failing alternator diode putting alternating ripple onto the vehicle's electrical system
- Cracked sensor mounting boss or fatigued bracket allowing the air gap to change under vibration
- Poor or corroding ground connection that behaves acceptably cold and badly once hot
Symptoms
- Engine stalls after twenty to thirty minutes of running and restarts once it has cooled
- Momentary cut-out at speed, followed by the engine picking up again on its own
- Intermittent hard starting with no discernible pattern to the owner
- Tachometer needle flicking to zero and back while the engine is running
- Check engine light that comes on, goes off again after a few journeys, and returns weeks later
- Random misfire codes stored alongside this one, set during the moments the signal was absent
Diagnostic steps
- 1.Read the freeze frame data before clearing anything. Coolant temperature, engine load and vehicle speed at the moment the code set usually separate a heat fault from a vibration fault immediately.
- 2.Ask the owner for the exact sequence of events. A stall after half an hour of driving followed by a successful restart once cool is close to a diagnosis on its own.
- 3.Run the engine to full operating temperature and then apply a heat gun to the sensor body while watching live engine speed on a scan tool. A reading that drops out as it heats identifies the sensor positively.
- 4.Follow up with freeze spray on the same sensor. A signal that returns as it cools confirms the finding rather than leaving it as an inference.
- 5.With the engine idling, wiggle the connector, the harness and the sensor itself in turn while watching live engine speed, so a mechanical break announces itself.
- 6.Inspect the harness along its whole run for chafe marks, especially where it passes a bracket or crosses the engine-to-body movement gap. Flex the suspect section rather than only looking at it.
- 7.Check for alternating ripple on the charging system with a scope or a meter that measures alternating volts on a direct current supply. A failing diode corrupts a marginal signal without failing any static test.
- 8.Note whether the signal wire runs near a high-tension lead or an aftermarket power cable, and try rerouting it away before condemning any component.
Repair cost
$130 – $800
Sensor replacement typically runs $130 to $450 once diagnosis is included, and diagnosis is a larger share of the bill on this code than on the others in the family because reproducing an intermittent fault takes real workshop time. Connector and harness repairs are $100 to $350. If the underlying cause turns out to be a failing alternator putting ripple onto the system, budget $400 to $800 for the alternator instead — and be glad it was found before a new sensor failed to fix anything.
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.