Manufacturer Code Charts: 1857
Ratio of HFM signal to intake manifold pressure is too high.
Possible cause:
- B28 (Pressure sensor)
- B2/5 (Hot film mass air flow sensor)
Affected functions:
- Engine output
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Test 1: Check component B2/5 (Hot film mass air flow sensor).
Test 2: Check component B28 (Pressure sensor).
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 B28 (Pressure sensor).
Test 2.1: Check component B28 (Pressure sensor) using actual value.
Test 2.2: Check power supply of component B28 (Pressure sensor).
Test 2.3: Test signal voltage of component B28 (Pressure sensor).
2.1. Check component B28 (Pressure sensor) using actual value.
Test sequence
- Switch on ignition.
Status of relevant actual value:
- Coolant temperature:Warning! Communication with ECU required.
- Intake manifold pressure (ADC):Warning! Communication with ECU required.
Specified values
- Coolant temperature > 80° C
- Intake manifold pressure,Ignition ON: > 3.5 V
- Intake manifold pressure,Operate engine at idling speed.:< 2 V
Question
- Is the actual value o.k.?
YES
The actual value is okay.End of test
NO
The actual value is not o.k.Possible cause and remedy
- Check power supply of component B28 (Pressure sensor).
- Test signal voltage of component B28 (Pressure sensor).
Further possible causes of fault
- Vacuum line
2.2. Check power supply of component B28 (Pressure sensor).
Figure legend
- B28 (Pressure sensor)
- 126/1 -'Secondary air injection left bank of cylinders' shutoff valve
Test prerequisite
- The actual value is not o.k.
Test sequence
- Switch off ignition.
- Detach coupling at component B28 (Pressure sensor).
- Measure direct voltage with multimeter between sockets (B28) 1 and (B28) 3
- Switch on ignition.
Specified value
- Voltage[4.75...5.25] V
Question
- Is the measurement value OK?
YES
The measurement value is OK.Further possible causes of fault
- Test signal voltage of component B28 (Pressure sensor).
NO
The measurement value is not OK.Possible cause and remedy
- Lines to component N3/10 (ME-SFI [ME] control unit)
End of test
2.3. Test signal voltage of component B28 (Pressure sensor).
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
Figure legend
- B28 (Pressure sensor)
- 126/1 -'Secondary air injection left bank of cylinders' shutoff valve
Test prerequisite
- The power supply of component B28 (Pressure sensor) is OK.
Test sequence
- Switch off ignition.
- Connect the vacuum tester to the input of component B28 (Pressure sensor) with the 3 x distributor.
- Connect socket box (126-pin) to component N3/10 (ME-SFI [ME] control unit).
- Measure direct voltage with multimeter between sockets [ M.15 ] 15 and [ M.86 ] 86 of the 126-pole socket box tester.
- Switch on ignition.
Specified values
- Ignition ON: >3.5 V
- Operate engine at idling speed.(Vacuum> 500 mbar):< 2 V
Question
- Are the measurement values OK?
YES
The measurement values are OK.End of test
NO
The measurement values are not OK.Possible cause and remedy
- Lines to component B28 (Pressure sensor)
- B28 (Pressure sensor)
Further possible causes of fault
- Vacuum line
End of test