Check Engine Lamp Circuit

170

TM 9-2320-312-24-2

Troubleshooting Section

Result 2 The change oil lamp did not turn

D. The test lamp should turn on. If the test lamp

does not turn on, either the test lamp is faulty or

on. The vehicle's lamp circuit is not functioning

the wiring to the ECM is faulty. Continue with this

properly. The lamp is probably burned out or

step if the lamp turns on.

there is a problem in the wiring from the cab to

either the ECM or the +battery connection. Repair

E. Leave the probe of the test lamp connected to

the lamp circuit or send the vehicle to the OEM

terminal 52 (unswitched +battery).

dealer for repairs. STOP.

Result 3

F. Connect the other probe of the test lamp to

terminal 30 (Output 1) of the breakout T.

Repair: Perform the following diagnostic

Refer to Illustration 44.

procedure:

G. Connect ET. Access the following display

The circuit between the ECM and the lamp is

screens in order:

shorted to chassis ground. Repair the circuit or

send the vehicle to the OEM dealer for repairs.

Diagnostics

STOP.

Diagnostic Test

Test Step 4. Check the Output Circuit of

the ECM.

Special Test

H. Activate the "Change Oil Lamp" test. Observe

the voltage test lamp. The lamp should turn on

when the test is active. Also, the lamp should

turn off when the test is inactive.

Expected Result:

The test lamp turns on and the test lamp turns off

per the above description.

Results:

Yes The ECM is operating correctly. There is a

problem in the vehicle wiring or the lamp. STOP.

Repair: Temporarily connect a test ECM. Check

the output circuit of the ECM that supplies power

to the change oil lamp when the test ECM is

installed. If the problem is resolved with the test

g00836186

Illustration 44

ECM, reconnect the suspect ECM. If the problem

Breakout T

returns with the suspect ECM, replace the ECM.

A. Disconnect ECM vehicle harness connector

STOP.

J1/P1.

B. Insert a 70-Terminal breakout T between ECM

i01631786

vehicle harness connector J1 and ECM vehicle

Check Engine Lamp Circuit -

harness connector P1.

Test

C. Connect one probe of the voltage test lamp to

terminal 65 (-battery). Connect the other probe of

SMCS Code: 7431-081

the voltage test lamp to terminal 52 (unswitched

+battery) of the breakout T.

System Operation Description:

Use this procedure under the following situation: