P1789
Symptom: Engine idling speed drops when the selector lever is moved from P or N.
Drive Signal. Open Circuit / Short to Ground.
Fault symptoms
Engine idling speed drops when the selector lever is moved from P or N.
Conditions
Short circuit to ground or open circuit.
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 output signal from the control module
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Connect a diagnostic tool.
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Turn the ignition to the ON position.
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Select "
Data Display / Output Control (New)".
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Select "
Drive Signal".
The diagnostic tool should read OFF with the selector lever in positions P and N, and ON with the selector lever in positions R, D, 3, 2, 1.
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Are the readings correct?
Continue with step 3.
Continue with step 2.
2. Check the input signal to the engine management system
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Unplug the connector from the engine control module.
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Turn the ignition to the ON position.
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Connect a test lamp to the connector as follows:
Motronic:
between pin 47 and pin 27
Trionic:
between pin 14 and pin 60
The test lamp should light up when the selector lever is in position P and N but not in other positions.
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Is the signal correct?
Continue fault diagnosis with Service Manual 2:7 "Engine Management System" and then go to step 3.
Rectify the relevant lead and continue with step 3.
3 Final check
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Clear all diagnostic trouble codes in the system.
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Perform a driving cycle:
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Drive the car at varying loads and engine speeds for 5 minutes.
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Evaluate the driving cycle:
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Make sure the trouble code has not recurred.
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Has the trouble code recurred?
Continue with “
Diagnostic procedure before replacing control module
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The steps taken to rectify the fault were correct.
