What a CKP sensor does and why it fails

The crankshaft position (CKP) sensor tells your engine's computer where the crankshaft is at any given moment. The engine uses this signal to time the spark plugs and fuel injectors. When the CKP sensor fails, the engine cannot fire at the right moment, so you get a rough idle, stalling, hard starting, or no start at all.

CKP sensors fail because they wear out over time — the magnetic coil inside degrades — or because they get dirty or corroded. Some fail because the reluctor ring (the toothed wheel the sensor reads) gets damaged. A few fail because the wiring harness gets pinched or corroded.

You can narrow down whether the CKP sensor is the problem by checking for a diagnostic trouble code, testing the sensor's output with a multimeter, and inspecting it for physical damage. This guide walks you through each step.

Key Takeaways

  • A CKP sensor that has failed will usually trigger a P0335 or P0336 trouble code, which you can read with an OBD-II scanner.
  • You can test a CKP sensor with a multimeter by measuring its resistance and AC voltage output while the engine cranks.
  • Visual inspection — looking for corrosion, cracks, or a loose connector — catches many failures before you need a meter.
  • The CKP sensor location varies by make and model; check your service manual or a repair database to find it on your vehicle.
  • A bad CKP sensor usually costs between $150 and $400 to replace, including labor, depending on how hard it is to reach.

Reading the diagnostic trouble code with an OBD-II scanner

The fastest way to know if the CKP sensor is the problem is to plug an OBD-II scanner into the diagnostic port under your steering wheel and read the trouble codes. A CKP sensor failure almost always sets a code in the P0335 to P0339 range. P0335 means "crankshaft position sensor circuit," P0336 means the signal is erratic, and P0337 or P0338 mean the signal is too low or too high.

You can buy an OBD-II scanner for $25 to $100, or borrow one from an auto parts store — many lend them free if you buy a sensor from them. Plug it in, turn the key to the "on" position without starting the engine, and scroll to "read codes." Write down the exact code number. If you see P0335, P0336, P0337, or P0338, the CKP sensor circuit is at fault. Other codes point to different problems.

If you see no codes at all but the engine still won't start or runs rough, the sensor may be failing intermittently, or the problem may be elsewhere. Move on to the visual inspection and multimeter test.

Locating and inspecting the CKP sensor

The CKP sensor sits near the crankshaft, usually on the engine block or transmission bell housing. On most vehicles it is within 12 inches of the crankshaft pulley. The exact location varies widely — some are straightforward to reach from the top of the engine, others require you to get under the car or remove the wheel.

Check your vehicle's service manual or search the year, make, and model on a repair database like AllData or Haynes to find the exact spot. Once you locate it, look for these signs of failure: corrosion or white/green oxidation on the connector, cracks in the plastic housing, oil or coolant leaking onto the sensor, a loose or corroded connector, or visible damage to the wiring.

If the connector is loose, push it firmly onto the sensor and try starting the engine. If the connector is corroded, disconnect it, clean both the connector and the sensor pin with a wire brush or fine sandpaper, and reconnect it. Many CKP sensor problems are actually loose or corroded connectors, not failed sensors.

Testing resistance with a multimeter

A multimeter is a handheld meter that measures voltage, current, and resistance. You can buy one for $15 to $50. To test the CKP sensor's resistance, disconnect the sensor connector, set the multimeter to the ohms (resistance) setting, and touch the meter's probes to the two pins on the sensor itself — not the connector.

Most CKP sensors have a resistance between 200 and 900 ohms, though the exact range depends on the make and model. Check your service manual for the correct range. If the meter reads infinity (no continuity) or zero, the sensor is open or shorted and has failed. If the reading is within range, the sensor's internal coil is intact, and the problem may be elsewhere.

Resistance testing tells you whether the coil inside the sensor is broken, but it does not tell you whether the sensor is generating the right signal while the engine runs. That requires the AC voltage test.

Measuring AC voltage while the engine cranks

The most reliable way to test a CKP sensor is to measure the AC voltage it produces while the engine is cranking. Set your multimeter to AC voltage (usually marked with a wavy line), set it to the 2-volt or 5-volt range, and touch the red probe to the signal wire on the sensor connector and the black probe to ground — a bare metal part of the engine block works.

Have someone crank the engine while you watch the meter. A working CKP sensor usually produces between 0.5 and 5 volts AC, depending on the make and model. If the meter reads zero or stays flat, the sensor is not generating a signal and has likely failed. If the voltage jumps around erratically or drops to zero while cranking, the sensor is intermittently failing.

Check your service manual for the exact voltage range your sensor should produce. If your reading is outside that range, the sensor has failed. If the reading is within range but the engine still will not start, the problem is likely in the wiring, the connector, or the engine computer, not the sensor itself.

Checking the wiring and connector

Before you replace the sensor, inspect the wiring harness and connector for damage. Look for pinched wires, cuts in the insulation, or corrosion inside the connector. Wiggle the connector while the engine is cranking and watch the multimeter — if the voltage jumps or drops when you move the wire, the connector or wiring is loose or corroded.

If the connector is corroded, disconnect it and clean both sides with a wire brush or fine sandpaper. If the wiring is damaged, you may be able to splice it or replace the connector. If the connector is cracked or the wire is severely damaged, the entire harness may need to be replaced.

A bad connector or corroded wire can mimic a failed sensor, so always check these before you buy a new sensor. Cleaning a corroded connector costs nothing and takes five minutes.

When to replace the CKP sensor

Replace the CKP sensor if the resistance test shows the coil is open or shorted, if the AC voltage test shows no signal or an erratic signal, or if you see physical damage to the sensor housing or wiring that cannot be repaired. If the connector was loose or corroded and you cleaned it, and the engine now starts and runs normally, the sensor is fine and does not need replacement.

Replacement usually takes 30 minutes to two hours, depending on how hard the sensor is to reach. Some sensors bolt on from the outside; others require removing the engine cover, wheel, or transmission pan. The sensor itself costs $30 to $150, and labor runs $100 to $300. If you are comfortable working on cars, you can replace it yourself and save the labor cost.

After you install a new sensor, clear the trouble codes with the OBD-II scanner and test-drive the vehicle. The engine should start easily, idle smoothly, and run without hesitation.

Frequently Asked Questions

Can a bad CKP sensor cause a check engine light?

Yes. A failed CKP sensor almost always triggers a check engine light and sets a trouble code in the P0335 to P0339 range. If your check engine light is on and you have not read the codes yet, that is the first step.

What happens if I drive with a bad CKP sensor?

The engine may not start, or it may start but stall when ready. If it does run, it will idle roughly, hesitate when you accelerate, and may cut out at highway speeds. Driving on a failing CKP sensor can damage the catalytic converter if the engine misfires repeatedly.

How do I know if it is the CKP sensor or the camshaft position sensor?

The CKP sensor trouble codes are P0335 to P0339. The camshaft position (CMP) sensor codes are P0010 to P0014. Read the codes with an OBD-II scanner to tell them apart. Both sensors can fail, but they trigger different codes.

Can I test the CKP sensor without removing it?

Yes. You can measure AC voltage at the connector while the engine cranks without removing the sensor. You can also check the connector for corrosion and the wiring for damage without taking anything apart. Remove the sensor only if the tests show it has failed or if you need to inspect the reluctor ring for damage.

What if the CKP sensor tests good but the engine still will not start?

If the sensor resistance and AC voltage are both within range, the problem is likely in the wiring, the connector, the engine computer, or a different sensor altogether. Have the wiring harness tested for continuity, check that the computer is receiving the signal, and read all trouble codes to look for other problems.