Crankshaft position sensors -Testing & Replacing On 99-00 Grand Am's

01-15-2007, 05:12 PM
Testing the crankshaft position sensor

This work is for Grand Am & Alero 99+,
Cutlass 97-99, Malibu 97-00
With engines, 2.4L 4cyl, and or the V6 3.1 & 3.4L

-- Performing these tests will set a diagnostic trouble code and illuminate the service engine light.
- Clear the codes after performing these tests and or repairs.

The crankshaft position sensor provides the ignition module and PCM a crank position signal.
The ignition module uses the signal to determine the firing order for each cylinder.
The PCM uses the signal to control the ignition timing and calculate RPM’s.
The signal is also used by the On board diagnostic (OBD) system to detect misfires.

-- The 4cyl has one 7X crankshaft position sensor (CPS).
-- The V6 has two CPSs a 7X and a 24X.

The 7X, on the 4cyl is located on the front (radiator)side of the engine , you cant actually see the sensor because its inside the motor reading the crankshaft, and on the V6 its on the rear(firewall)side of the engine, the 24X is on the Crankshaft behind the harmonic balancer(Crankshaft Pulley).

Pic of 7X on 4 cylinder (

7X on the V6 (

The 7X CPS is a magnetic inductive sensor triggered by 7 slots cut into a reluctor ring on the crankshaft.
The sensor tip is about .05 inches from the reluctor ring.
As the notches pass the sensor the magnetic field is changed producing a pulsating voltage signal 7 times (7X) per crankshaft revolution.

The 24X CPS sensor is a hall effect device triggered by an interrupter ring behind the crankshaft pulley.
This sensor produces on and off pulses as the 24 blades and windows of the interrupter pass through the magnetic field.
The ignition system won’t work if the PCM doesn’t receive a 7X signal.

To test the 7X sensor, disconnect the plug connector.
Theirs also two wires for this at the ignition control module.
- A purple wire and a yellow wire, they need to be tested in AC volts.
- When cranking over the engine it should read at least 200 millivolts, if not replace the 7X sensor.

The 24X is on the front of the engine (on the oil pan) beside the crankshaft pulley,
which reads the interrupter ring in the harmonic balancer.

24X on V6 (

First check for power from the PCM.
- Disconnect the plug in, connect the positive on the voltmeter to the red/white wire and the ground to the black wire terminal turn the key on and it should be 12vlts, if not check the wiring from the 24X to the PCM.

CPS wiring harness location (

To check for operation is a bit more involved, reconnect the plug in.
- Using a probe, back probe the light blue/black wire terminal of the CPS and connect the positive lead of the voltmeter to the probe and the negative to an engine ground.
- Turn the key on, it should be about 10 volts.
- Now rotate the engine slowly (by hand) with a breaker bar and socket on the crankshaft bolt.
- While reading the voltmeter it should read between 10 – 0 volts as the blades pass the interrupter ring passed the CPS.
- If it’s not with in those tolerances, replace the 24X CPS.

To make turning the engine over by hand easier, remove the spark plugs first.

Crankshaft position sensor replacement

**Any time a CPS is replaced, you may have to do a learning procedure,
or the system might give a false Diagnostic trouble code (DTC).
If your car has thrown a DTC call a dealer, or other qualified tech for this procedure.

To replace the 7X sensor disconnect the wiring harness connector.
Remove the CPS mounting bolts and pull the sensor out of the engine block.
Replace the “O” ring lightly lube it with clean oil.
- Install in the reverse procedure.

To replace the 24X sensor remove the drive belt.
- Jack up the vehicle and support with jack stands.
- Remove the crankshaft pulley.
- Remove the bolt and sensor wiring harness retainer bracket.
- Remove the 24X CPS mounting bolts.
- Remove the sensor and pull out the wiring harness,
Paying attention to how and where the harness was routed.

Any further questions PM me,
or post your troubles in the N-Body Problem Diagnosis (

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