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Home >> Mercedes Benz >> 2007 >> CLK 550 Cabriolet (209.472) V8-5.5L (273.967) >> Repair and Diagnosis >> A L L Diagnostic Trouble Codes ( DTC ) >> Testing and Inspection >> P Code Charts >> P0068

P0068


The measured air mass is implausible compared to the position of the throttle valve. (P0068)


Possible cause:

- B2/5 (Hot film mass air flow sensor)
- M16/6 (Throttle valve actuator)
Affected functions:

- Engine diagnosis
- Engine output

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Test 1: Check component B2/5 (Hot film mass air flow sensor).

Test 2: Check component M16/6 (Throttle valve actuator).

1. Check component B2/5 (Hot film mass air flow sensor).

Test 1.1: Check signal of component B2/5 (Hot film mass air flow sensor) via actual value with engine OFF.

Test 1.2: Check signal of component B2/5 (Hot film mass air flow sensor) via actual value with engine speed greater than 3500 rpm.

Test 1.3: Check reference signal of component B2/5 (Hot film mass air flow sensor).

Test 1.4: Check power supply of component B2/5 (Hot film mass air flow sensor).

1.1. Check signal of component B2/5 (Hot film mass air flow sensor) via actual value with engine OFF.
Warning!Communication with ECU required.


1.2. Check signal of component B2/5 (Hot film mass air flow sensor) via actual value with engine speed greater than 3500 rpm.
Warning!Communication with ECU required.


1.3. Check reference signal of component B2/5 (Hot film mass air flow sensor).
Test sequence

- Switch on ignition.
Status of relevant actual value:
- HFM-SFI ( Reference signal ):Warning! Communication with ECU required.
Specified value

- Reference signal[46...59] ms
Question

- Is the measurement value OK?


YES
The actual value is okay.End of test

NO
The actual value is not o.k.Possible cause and remedy

- Check lines from component N3/10 (ME-SFI [ME] control unit) to component B2/5 (Hot film mass air flow sensor).
- B2/5 (Hot film mass air flow sensor)


1.4. Check power supply of component B2/5 (Hot film mass air flow sensor).
Image legends

- B2/5 (Hot film mass air flow sensor)
- Connector (5-pin)
Test prerequisite

- The actual value is not o.k.
Test sequence

- Switch off ignition.
- Detach coupling at component B2/5 (Hot film mass air flow sensor).
- Measure direct voltage with multimeter between sockets (B2/5) 2 and (B2/5) 1
- Switch on ignition.
Specified value

- Voltage[11.0...15.0] V
Question

- Is the measurement value OK?







YES
The actual value is okay.Further possible causes of fault

- Unmetered air
- Signal wire
- B2/5 (Hot film mass air flow sensor)
End of test

NO
The measurement value is not OK.Possible cause and remedy

- N10/1f43 (Fuse 43)
- Cable for voltage supply
End of test

2. Check component M16/6 (Throttle valve actuator).

Test 2.1: Test voltage supply of the potentiometers of component M16/6 (Throttle valve actuator).

Test 2.2: Check component M16/6 (Throttle valve actuator) using actual value.

Test 2.3: Check component M16/6m1 (Actuator motor) by means of actuation.

Test 2.4: Check internal resistance of component M16/6m1 (Actuator motor).

Test 2.5: Check internal resistance of component M16/6 (Throttle valve actuator).

2.1. Test voltage supply of the potentiometers of component M16/6 (Throttle valve actuator).
Test prerequisite

- At least one of the relevant actual values is not okay.
- The power supply of component N3/10 (ME-SFI [ME] control unit) is OK.
Test sequence

- Switch off ignition.
- Connect socket box (126-pin) to component N3/10 (ME-SFI [ME] control unit).
- Measure direct voltage with multimeter between sockets (M.39) 39 and (M.43) 43 of the 35-pole socket box tester.
- Switch on ignition.
Specified value

- Voltage[4.75...5.25] V
Question

- Is the measurement value OK?


YES
The measurement value is OK.Possible cause and remedy

- Check lines from component M16/6 (Throttle valve actuator) to component N3/10 (ME-SFI [ME] control unit).
End of test

NO
The measurement value is not OK.Possible cause and remedy

- N3/10 (ME-SFI [ME] control unit)
End of test

2.2. Check component M16/6 (Throttle valve actuator) using actual value.
Warning!Communication with ECU required.


2.3. Check component M16/6m1 (Actuator motor) by means of actuation.
Test prerequisite

- Operate engine at idling speed.
Note

- If the throttle valve angle is< 1,1°, unmetered air may be present.
Status of relevant actual value:
- Throttle valve angle:Warning! Communication with ECU required.
Move on to actuation with button F2

2.4. Check internal resistance of component M16/6m1 (Actuator motor).
Figure legend

- A -ConnectionTest cable 35-pin socket box
- 001 -Sockets of component N3/10 (ME-SFI [ME] control unit)
- 05 -35-pin socket box
- 050 -126-pin socket box
- 108 -Test cable 266 589 01 63 00
- N3/10 (ME-SFI [ME] control unit)
- II 1-63ConnectionTest cable
- III 64-126ConnectionTest cable
Warning!

- Connection A of test cable 108 may NOT be connected to connection B of the 126-pin socket box (050).
Continue to test with button F2







Test sequence

- Switch off ignition.
- Disconnect coupling M at component N3/10 (ME-SFI [ME] control unit).
- Measure resistance with multimeter between sockets (M.75) 75 and (M.74) 74 of the 126-pole socket box tester.
Specified value

- Resistor[1...10]ohms
Question

- Is the measurement value OK?


YES
The measurement value is OK.End of test

NO
The measurement value is not OK.Possible cause and remedy

- Lines between N3/10 (ME-SFI [ME] control unit) and M16/6m1 (Actuator motor)
- M16/6m1 (Actuator motor)
End of test

2.5. Check internal resistance of component M16/6 (Throttle valve actuator).
Figure legend

- A -ConnectionTest cable 35-pin socket box
- 001 -Sockets of component N3/10 (ME-SFI [ME] control unit)
- 05 -35-pin socket box
- 050 -126-pin socket box
- 108 -Test cable 266 589 01 63 00
- N3/10 (ME-SFI [ME] control unit)
- II 1-63ConnectionTest cable
- III 64-126ConnectionTest cable
Warning!

- Connection A of test cable 108 may NOT be connected to connection B of the 126-pin socket box (050).
Continue to test with button F2







Test prerequisites

- The throttle flap of component M16/6 (Throttle valve actuator) should operate freely and must not stick or rub.
- At least one of the relevant actual values is not okay.
Test sequence

- Switch off ignition.
- Remove component B2/5 (Hot film mass air flow sensor).
- Disconnect coupling M at component N3/10 (ME-SFI [ME] control unit).
M16/6r3 (Actual value potentiometer (sliding contact 1))

- Measure resistance with multimeter between sockets (M.88) 88 and (M.43) 43 of the 126-pole socket box tester.
- Slowly operate throttle flap by hand up to full load.
Specified values

- Throttle valve not actuated[ca. 1380]ohms
- Throttle valve fully actuated[ca. 480]ohms
M16/6r4 (Actual value potentiometer (sliding contact 2))

- Measure resistance with multimeter between sockets (M.64) 64 and (M.43) 43 of the 126-pole socket box tester.
- Slowly operate throttle flap by hand up to full load.
Specified values

- Throttle valve not actuated[ca. 650]ohms
- Throttle valve fully actuated[ca. 1490]ohms
Question

- Are the measurement values OK?


YES
The measurement values are OK.Further possible causes of fault

- Test voltage supply of the potentiometers of component M16/6 (Throttle valve actuator).


NO
The measurement values are not OK.Possible cause and remedy

- Lines to component M16/6 (Throttle valve actuator)
- M16/6 (Throttle valve actuator)
End of test

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