P1140
MASS AIR FLOW SENSOR/THROTTLE POSITION SENSOR, MALFUNCTIONING
Fault Symptoms
CHECK ENGINE lamp (MIL) on. Performance down/reduced driveability.
Possibly other diagnostic trouble codes.
Conditions.
P1140
^ Coolant temperature above 60°C (140°F).
^ Engine speed higher than 1320 rpm.
^ Time since starting more than 35 seconds.
^ The mass air flow sensor's value does not coincide with the value from the throttle position sensor for more than 7 seconds.
Diagnostic Help.
A reading of the mass air flow sensor's performance can be obtained with the Tech 2.
- Turn off all electrical equipment. On cars with
automatic transmission, move the selector lever to position N or P.
- Connect the Tech 2 and start the engine.
- Select "MASS AIR FLOW SENSOR".
Check that the Tech 2 shows the following air mass as a function of engine rpm:
^ idling speed (about 0.8 V)
^ at 2500 rpm (about 1.5 V)
Slightly higher values will be obtained with a cold engine.
A reading of the throttle position sensor's performance can be obtained with the Tech 2.
- Turn the ignition switch to the ON position.
- Select "THROTT POS SENSOR".
If the throttle position information is OK, the Tech 2 should show activated throttle position readings of 0.5-4.5V from unactuated to fully depressed accelerator (from closed throttle position to wide open throttle).
Check The Wiring.
Intermittent faults may occur as a result of occasional short circuits and breaks in the wiring. Jiggle the leads and in-line connectors at several
places and in different directions to reveal faults in the wiring harness. Observe the multimeter, Tech 2 diagnostics instrument or test lamp while carrying out this check.
Diagnostic Procedure.
1. Check fuel adaptation
- Connect the Tech 2.
- Check whether:
^ Additive adaptation is higher than � 0.2 ms.
^ Multiplicative adaptation is higher than �10%.
Are either of the values exceeded
YES
^ Continue with point 2.
NO
^ Continue with point 5.
2. Check for air leakage
- Inspect hoses/connections between the mass air flow sensor and the throttle body for leakage.
Function OK?
YES
^ Continue with point 3.
NO
^ Rectify any faults. Continue with point 7.
3. Check the mass air flow sensor's ground connection and power supply
- Unplug the mass air flow sensor's 4-pin connector.
- Turn the ignition switch to the ON position.
- Connect the test lamp to the connector between:
^ B+ and pin 1
^ B+ and pin 2
^ Pin 3 and battery negative (B-)
The test lamp should light up in all 3 cases.
Function OK?
YES
^ Continue with point 4.
NO
^ Repair or replace the relevant lead.
Continue with point 7.
4. Check the control module's mass air flow sensor input
- Connect a conventional 1.5 V battery (in good condition) as follows:
^ Battery positive to pin 4
^ Battery negative to pin 2
- Turn the ignition switch to the ON position.
- Select "MASS AIR FLOW SENSOR".
The Tech 2 should show a reading of about 1.5 V.
Function OK?
YES
^ Change the mass air flow sensor.
Continue with point 7.
NO
^ Check the relevant lead and repair or replace it if
necessary. Continue with point 7.
5. Check the throttle position sensor's ground connection and power supply
- Unplug the throttle position sensor's 3-pin connector.
- Turn the ignition switch to the ON position.
- Take voltage readings on the connector contacts as follows:
^ pin 1 and B- (about 5 V)
^ B+ and pin 2 (B+)
Function OK?
YES
6 Continue with point 6.
NO
^ Check the relevant lead and repair or replace it if necessary. Continue with point 7.
6. Check the control module's throttle position sensor input
- Connect the Tech 2.
- Turn the ignition switch to the ON position.
- Read "THROTT POS SENSOR".
The Tech 2 should show a reading of about 5 V.
- Connect a jumper lead in the throttle position sensor's connector between:
^ pins 1 and 3
The Tech 2 should show a reading of 0 V.
Function OK?
YES
^ Change the throttle position sensor.
Continue with point 7.
NO:
^ Repair or replace the relevant lead. Continue with point 7.
7. Final check
- Clear the diagnostic trouble code.
- Implement a driving cycle:
^ Drive the car at varying engine loads and rpm for 5 minutes.
- Evaluate the driving cycle:
^ Check whether the diagnostic trouble code has recurred.
Has the diagnostic trouble code recurred?
YES
^ Continue with "Before Replacing A Control Module". Component Tests and General Diagnostics
NO
^ The steps taken to rectify the fault were correct.