P0320
- Powertrain
- Generic (SAE)
- Emissions
Get it looked at now
This signal governs whether the engine runs at all. The realistic failure mode is a stall without warning — in traffic, in an intersection, or at highway speed — where steering effort rises sharply and the brake booster loses vacuum after about one or two pedal applications, leaving brakes that still work but demand far more pedal force. That is a safety concern, not just a drivability one.
- Safe to drive
- Treat as unsafe to drive. Sudden stalling is the expected failure. Have it towed or repaired before further use.
Ignition/Distributor Engine Speed Input Circuit
The computer lost or could not trust the engine speed signal it uses to know how fast the crankshaft is turning and when to fire the spark. Without a trustworthy speed reference the engine may crank without starting, or stall while running.
P0320 reports a circuit or plausibility fault on the ignition-side engine speed reference input. On older distributor systems this is the pickup coil or optical sensor inside the distributor, or the tach reference from an external ignition module. On distributorless systems it is the crank-derived RPM reference delivered to the ignition control function. The code covers open circuit, short circuit, and signal-present-but-implausible conditions, and the manufacturer decides which of those apply.
How the car detected itThe module expects a pulse train whose frequency tracks engine speed. It sets this code when the input is absent while other evidence says the engine is turning, when pulse timing is erratic or noisy, or when the reference disagrees with a second speed source the module can cross-check. Because the signal is the timing backbone for spark, a fault here is often detected within a fraction of a second and can force a shutdown of ignition and injection.
A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.
- Safe to drive
- Treat as unsafe to drive. Sudden stalling is the expected failure. Have it towed or repaired before further use.
- Urgency
- Get it looked at now
- Will it pass emissions
- No
- If ignored
- Expect intermittent stalling that becomes frequent, followed by a no-start that leaves the vehicle wherever it happens to be. In a stall at speed, steering effort rises sharply and the brake booster loses vacuum after about one or two pedal applications, leaving brakes that still work but demand far more pedal force. If the cause is a chafed harness, continued vibration turns an intermittent open into a hard short that can damage the module driver.
- Check engine light
- Solid
These are the causes this code can have. For the order to work through them in, see what to check first.
| # | Cause | How often | Component |
|---|---|---|---|
| 1 | Sensor or pickup failed | Very common | — |
Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.
In order. Each of these is cheaper or faster than what follows it, and each one can make the rest unnecessary.
Does the tachometer sweep while cranking
A dead tach during crank is direct evidence the speed reference never reaches the module. It costs nothing and immediately narrows the search.
Engine RPM PID on a scan tool during cranking
More reliable than the dash tach because it reads the value the module actually has. Zero or wildly jumping RPM while cranking confirms the input is the problem.
The sensor or distributor connector and the harness within a foot of it
Heat, oil, and vibration kill these connectors. Green pins, oil-soaked terminals, or a chafed wire against a bracket are common and cheap to find.
Power and ground at the sensor with the key on, if the sensor is a powered type
If the sensor is a powered type (three-wire Hall or optical), it cannot produce a signal without its supply and ground, and verifying those first prevents the most common wasted part on this code. A two-wire variable-reluctance pickup has no supply — it generates its own AC signal — so on that design verify the two signal conductors and the shield instead.
Whether an aftermarket alarm, remote start, or stereo amplifier has been spliced into engine harness circuits
Aftermarket taps into the tach or ignition circuits are a frequent source of noise and intermittent opens that produce exactly this code.
Confirm the fault condition and capture freeze frame
Tools Scan tool
Note whether the code sets on a no-start, on a stall, or while running normally. Try to reproduce it — cold, hot, over bumps, at a specific speed. An intermittent that only appears hot behaves very differently from a hard open.
ExpectedA repeatable trigger condition you can test against
Monitor engine speed on a scan tool while cranking
Tools Scan tool
Crank the engine and watch the RPM PID. Compare it against what the tachometer shows. If the module reports zero RPM while the starter turns the engine, the input signal is missing or unusable.
ExpectedA steady cranking RPM reading, typically a few hundred RPM. Zero or erratic is the finding.
Scope the sensor signal at the sensor connector
Tools Oscilloscope, back-probe leads, wiring diagram
Back-probe the signal line and crank. This is the definitive test and it distinguishes a dead sensor from a broken wire between sensor and module. A variable-reluctance pickup produces an AC waveform whose amplitude grows with speed; a Hall or optical sensor produces a square wave. Which type your vehicle uses varies by make and year.
ExpectedA clean, consistent pulse train synchronized to engine rotation, with no dropouts or noise
Identify the sensor type, then verify supply, ground, winding, and shield accordingly
Tools DMM, wiring diagram
First identify the sensor type from the wiring diagram. On a powered Hall or optical sensor, confirm reference or battery voltage at the supply pin with the key on, then check ground quality — voltage drop from the ground pin to battery negative with the circuit live, or a resistance check with the key off and the circuit unpowered. On a two-wire variable-reluctance pickup there is no supply pin; instead measure winding resistance against service data and check the shield. Many of these circuits use a shielded cable — an open or improperly grounded shield lets ignition noise corrupt the signal.
ExpectedOn a powered sensor, supply within a few tenths of the specified reference and a ground path under about 0.1 V drop, or under about an ohm measured unpowered. On a VR pickup, winding resistance within the service specification. Exact values are vehicle-specific.
Test harness continuity and insulation between sensor and module
Tools DMM, wiring diagram
Disconnect both ends. Check each conductor for continuity end to end, for shorts to ground, and for shorts to each other and to voltage. Then wiggle-test the harness along its full run while watching the meter.
ExpectedContinuity on each conductor, no shorts, and no reading change during the wiggle test
Inspect the trigger mechanism itself
Tools Hand tools, inspection light, dial indicator for shaft play
On a distributor system, check the pickup coil, optical disc, and shaft for oil contamination, wear, and excessive shaft play. Oil on an optical disc is a well-known cause of this fault on distributor-equipped vehicles. On a distributorless system, inspect the reluctor ring and the sensor tip for damage and debris.
ExpectedA clean trigger surface, an intact disc or reluctor, and minimal shaft play. Play limits are vehicle-specific.
Check for electrical noise from aftermarket accessories
Tools Oscilloscope, DMM with AC volts
If the signal scopes clean at the sensor but the module reports implausible speed, look for aftermarket wiring spliced into the harness, poorly routed plug wires laid across the sensor lead, or a failing alternator injecting AC ripple into the supply.
ExpectedMinimal AC ripple on the charging system and no signal corruption when accessories are disconnected
Consider the control module only after the circuit is proven
Tools Oscilloscope, DMM, wiring diagram
If a clean, correct signal arrives at the module connector and the module still reports the fault, the input circuit inside the module is suspect. Verify the module's own power and grounds first — a bad module ground mimics module failure.
ExpectedGood signal in, good power and grounds, and a persistent fault points to the module
| Repair | Only after you confirm | Typical cost | Who |
|---|---|---|---|
| Replace the distributor pickup, optical sensor, or the distributor assembly | Scope shows no signal or a corrupted signal at the sensor connector, with supply and ground confirmed good on a powered design, or winding resistance out of specification on a two-wire pickup | $200–$900 | DIY |
| Replace the crankshaft position sensor supplying the speed reference | No usable waveform at the sensor with the circuit verified for its sensor type, or the signal drops out when the sensor is heated | $130–$480 | DIY |
| Repair or replace the connector, terminals, or a chafed harness section | Wiggle test changes the signal, or continuity and insulation testing finds an open, short, or high-resistance connection | $90–$450 | DIY |
| Repair or reground the signal cable shield or a corroded engine ground | Signal noise present at the module but clean at the sensor, and the shield or ground path measures open or high resistance | $90–$350 | DIY |
| Remove or correct aftermarket wiring spliced into the ignition or tach circuits | The fault disappears when the aftermarket device is disconnected | $100–$500 | DIY |
| Replace the ignition module or the engine control module | Correct signal confirmed at the module connector with verified module power and grounds, and the fault persists | $400–$1,900 | Shop |
US independent-shop ranges, parts plus labour. Diagnosis is the variable cost here — an intermittent that only appears when hot can take two or more hours to reproduce and is worth paying for rather than guessing at parts. Control module replacement often requires programming or immobilizer relearn, which adds labour or a dealer visit.
- Replacing the distributor or sensor first. The wiring, connector, and grounds fail at least as often and cost far less.
- Hunting for a supply voltage on a two-wire variable-reluctance pickup, which is self-generating and has no supply pin, then condemning wiring that was never at fault.
- Testing only with the engine off. Intermittent faults in this circuit are usually heat- or vibration-dependent and will not show on a static resistance check.
- Using a multimeter alone on a pulse signal. A meter averages and can read plausible while the waveform has dropouts a scope would show instantly.
- Overlooking aftermarket alarm or remote-start splices, which are a well-known source of intermittent faults on this circuit.
- Condemning the module without first verifying its own power and ground circuits.
- Assuming the sensor is in a particular location or that the connector pinout matches another vehicle. Both vary by make, model, and year.
- Crankshaft Position Sensor
- Ignition Distributor
- Definition
- Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.
- Diagnostic guidance
- Written and reviewed in-house. See our editorial policy.
- Review status
- Reviewed
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