P1790

Symptom: No downshifting when accelerating quickly.

P1790

Fault symptoms

No downshifting when accelerating quickly.

Conditions

Short circuit to ground while throttle position is less than 70% for at least 2 seconds.

Diagnostic help

The state of the kickdown switch can be read with the diagnostics tool.

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

Select " Kick-Down Switch".

With the accelerator pedal fully depressed, i.e. kickdown, ON will be displayed, otherwise OFF.

Diagnostic procedure

1 Check the control module signal input

-	Unplug the kickdown switch connector.

-	Connect a diagnostic tool.

-	Turn the ignition to the ON position.

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

-	Select " Kick-Down Switch".

Read the diagnostic tool with

•	connector pin 1 open "OFF"

•	connector pin 1 connected to a good grounding point "ON"

Are the diagnostic tool readings correct?

Yes

Continue with step 3.

no

Rectify the lead (including connector) between the kickdown switch connector pin 1 and the control module pin 8 and continue with step 2.

2 Check the kickdown switch ground connection

-	Turn the ignition to the ON position.

-	Connect a test lamp between connector pins 1 and 2. The lamp should light up.

Is the lamp alight?

Yes

Adjust or, if necessary, replace the kickdown switch and continue with step 3.

no

Rectify the lead (including connector) between the kickdown switch connector pin 2 and grounding point G4, and continue with step 3.

3 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.