Engine Speed/Timing Sensor Circuit

254

TM 9-2320-312-24-2

Troubleshooting Section

The engine uses two engine speed/timing sensors.

G. Access the special test "Engine Running Output"

Both of the engine speed/timing sensors detect

on ET.

the reference for engine speed and timing from

a unique pattern on the camshaft gear. The ECM

H. Cycle the special test "Engine Running Output"

counts the time between pulses that is created by

to "Active" and to "Not Active" and watch the

the sensor as the gear rotates in order to determine

voltage test lamp.

rpm. The ECM remembers the pattern of the pulses.

The ECM uses the pattern of the pulses in order to

I. Stop the special test.

determine the position of the crankshaft.

Note: A multimeter can not be used in place of the

When the timing has been established, the ECM

voltage test lamp when the ECM outputs are being

triggers each injector in the correct firing order at

tested.

the correct time.

Expected Result:

The actual timing and duration of each injection is

based on engine rpm and load. If the engine is

The voltage test lamp turns ON when the test is

running and the signal from one of the camshaft

active. The voltage test lamp turns OFF when the

position sensors is lost, no noticeable change in

test is not active.

engine performance will be noticed.

Results:

The engine will start and the engine will run when

Yes The ECM is OK. The problem is in the

only one sensor signal is present from either of the

sensors. The loss of the signal from both of the

vehicle wiring. Inspect the vehicle wiring and then

sensors during engine operation will result in the

repair the vehicle wiring. Otherwise, send the

termination of injection and the shutting down the

vehicle to the OEM dealer for repair. Verify that

engine by the ECM. The loss of the signal from

the original condition is resolved. STOP.

both of the sensors during start-up will prevent the

No Temporarily connect a test ECM. Use the

engine from starting.

"Engine Running Output Special Test" on ET to

Both sensors are magnetic sensors. The two

check the ECM. If the problem is resolved with

sensors are not interchangeable. Do not switch

the test ECM, install the suspect ECM. If the

the positions of the sensors. The two sensors

problem returns with the suspect ECM, replace

must be replaced as a pair. If the sensors are

the ECM. Verify that the repair eliminates the

replaced, a timing calibration is not necessary for

problem. STOP.

the engine. Timing calibration is only necessary

after replacing an ECM that will not communicate.

i01857873

Engine Speed/Timing Sensor

Circuit - Test

SMCS Code: 1912-081

System Operation Description:

Use this procedure under the following situation:

Use this procedure to troubleshoot the system only

under the following conditions:

There is an active diagnostic code or an easily

repeated diagnostic code that is associated with

the engine speed/timing circuit.

You have been referred to this test from

Troubleshooting, "Troubleshooting without a

Diagnostic Code".

g00864785

Illustration 90

The following background information is related

Left side engine view (typical view)

to this procedure: