P1842

Symptom: CHECK GEARBOX warning lamp on. TCM in Limp-Home mode. Torque limitation request absent, which results in harsh shifting.

P1842

Fault symptoms

CHECK GEARBOX warning lamp on.

TCM in Limp-Home mode.

Torque limitation request absent, which results in harsh shifting.

Conditions

Short circuit to ground or open circuit.

Diagnostic help

The torque limitation function can be controlled with the diagnostic tool.

Select " Data Display / Output Control (New)".

Select " Torque Limitation".

With the selector lever in position N and the engine unloaded at a speed of over 3000 rpm, the engine speed should momentarily drop to approx. 2500 rpm and then stabilize again.

Check the wiring

Jiggle the wiring harness at several points and in different directions to reveal intermittent breaks and short circuits in the various leads. Observe the multimeter, test lamp or diagnostic instrument while carrying out this check.

Diagnostic procedure

1 Check the signal to the engine management system

-	Connect the BOB to the transmission control module connector but without connecting the control module.

-	Turn the ignition to the ON position.

-	Take a voltage and current reading between pin 13 and pin 22. The nominal values are approx. B+ and approx. 8 mA respectively.

Are the readings correct?

Yes

Change the control module.

no

Rectify the relevant lead and continue with step 2.

2 Final check

-	Clear all diagnostic trouble codes in the system.

-	Perform a driving cycle:

•

Drive the car at varying loads and engine speeds for 5 minutes.

-	Evaluate the driving cycle:

•

Make sure the trouble code has not recurred.

Has the trouble code recurred?

Yes

Continue with Diagnostic procedure before replacing control module .

no

The steps taken to rectify the fault were correct.