Operation CHARM: Car repair manuals for everyone.
Home >> Volvo >> 1995 >> 960 L6-3.0L VIN 95 B6304F >> Repair and Diagnosis >> A L L Diagnostic Trouble Codes ( DTC ) >> Testing and Inspection >> Manufacturer Code Charts >> EFI / DTC Codes (Engine Control System) >> DTC 1-2-1

DTC 1-2-1

1-2-1 MASS AIR FLOW SENSOR SIGNAL




Trouble Code Conditions
If the signal from the Mass Air Flow (MAF) Sensor is less than 2.0 volts or greater than 5.3 volts and engine speed is higher than 200 rpm, the Engine Control Module (ECM) notes it as a fault and sets Diagnostic Trouble Code (DTC) 1-2-1.

Substitute value(s)
- The ECM uses engine speed and throttle opening to determine load.
- Idle Air Control (IAC) Valve adaption inhibited.
- Fuel trim adaption inhibited.

Fault source(s)
Signal too high:
- Signal lead short circuit to live.
- Break in signal/ground lead.
- Break in power/ground lead.
- Contact resistance in terminals.
- MAF sensor defect.

Signal too low:
- Signal lead short circuit to ground.
- Signal lead broken.
- Power lead broken.
- Contact resistance in terminals.
- MAF sensor defect.

Fault symptom(s)
- Engine misfiring.

TEST PROCEDURE




STATUS REPORT
^ Permanent fault, signal too high:
- Proceed to: PERMANENT FAULT, SIGNAL TOO HIGH section below.

^ Permanent fault, signal too low:
- Proceed to: PERMANENT FAULT, SIGNAL TOO LOW section below.

^ Intermittent fault, signal too high:
- Proceed to: INTERMITTENT FAULT, SIGNAL TOO HIGH section below.

^ Intermittent fault, signal too low:
- Proceed to: INTERMITTENT FAULT, SIGNAL TOO LOW section below.




PERMANENT FAULT, SIGNAL TOO HIGH
Check signal ground
- Ignition off.
- Disconnect MAF sensor.
- Connect an ohmmeter between terminal 1 of MAF sensor connector and ground.

The ohmmeter should read approx. 0 ohms.

If value OK:
^ Check power ground. Proceed to CHECK POWER GROUND section below.

If value differs:
^ Check connector. Proceed to CHECK CONNECTOR section below.




CHECK CONNECTOR
- Ignition off.
- MAF sensor disconnected.
- Check ECM connector and 55-pin connector in central relay unit (A3/E) terminal 13 for contact resistance and oxidation.
- ECM connected.



- Connect an ohmmeter between MAF sensors connector terminal 1 and ground.

The ohmmeter should read approx. 0 ohms.

If value OK:
^ Source of DTC is bad contact in connector.

If value differs:
^ Check lead between MAF sensor terminal 1 and ECM # 19 as well as lead between MAF sensor terminal 1 and control point 31/33 for break.




CHECK POWER GROUND
- Ignition off.
- MAF sensor disconnected.
- Connect an ohmmeter between terminal 2 on MAF sensor connector and ground.

The ohmmeter should read approx. 0 ohms.

If value OK:
^ Check signal lead. Proceed to CHECK SIGNAL LEAD section below.

If value differs:
^ Check ECM connector. Proceed to CHECK ECM CONNECTOR section below.




CHECK ECM CONNECTOR
- Ignition off.
- MAF sensor disconnected.
- Check ECM connector for contact resistance and oxidation.
- ECM connected.



- Connect an ohmmeter between MAF sensors connector terminal 2 and ground.

The ohmmeter should read approx. 0 ohms.

If value OK:
^ Source of DTC is bad contact in ECM connector.

If value differs:
^ Check lead between ECM # 26 and MAF sensor terminal 2 for break.




CHECK SIGNAL LEAD
- Ignition on.
- MAF sensor disconnected.
- Connect a voltmeter between MAF sensors connector terminal 3 and ground.

The voltmeter should read 0 - 0.5 volts.

If value OK:
^ Check IAC sensor signal. Proceed to CHECK IAC SENSOR SIGNAL section below.

If value differs:
^ Check lead between ECM # 7 and MAF sensor terminal 3 for short circuit to live.
^ After action: Check MAF sensor. Proceed to CHECK MAF SENSOR section below.

CHECK IAC SENSOR SIGNAL
- Ignition on.
- Erase DTC.
- Start and warm up engine.
- Gear selector: Neutral, A/C: off.
- Power consumers such as engine coolant fan, heated rear window, etc.: off.
- Enter parameter list.



- Read off load signal.

Value should be 2.3 - 2.4 volts at idle.

If value OK:
^ Source of DTC is bad contact in MAF sensors and/or ECM connector. Check connectors for contact resistance and oxidation.

If value differs:
^ Test with new MAF sensor.

NOTE: Check in Diagnostic Test Mode (DTM) 1 for automatic transmission whether DTC for load signal is triggered.

CHECK MAF SENSOR
IAC sensor can break down as a sequential fault resulting from a break in the signal ground or if the signal lead is short circuited to live.

- Ignition on.
- Erase DTC.
- Start and warm up engine.
- Gear selector: neutral, A/C: off.
- Power consumers such as engine coolant fan, heated rear window, etc.: off.
- Enter parameter list.



- Read off load signal.

Values should be 2.3 - 2.4 volts at idle.

If value differs:
^ Test with new MAF sensor.

NOTE: Check in Diagnostic Test Mode (DTM) 1 for automatic transmission whether DTC for load signal is triggered.

PERMANENT FAULT, SIGNAL TOO LOW
Check power lead
- Ignition off.
- Disconnect MAF sensor.
- Ignition on.



- Connect a voltmeter between MAF sensors connector terminal 5 and ground.

The voltmeter should read battery voltage.

If value OK:
^ Check signal lead. Proceed to CHECK SIGNAL LEAD section below.

If value differs:
^ Check lead between MAF sensor terminal 5 and fuse 5 (11B/5) in central relay unit for break.




CHECK SIGNAL LEAD
- Ignition off.
- MAF sensor disconnected.
- Connect an ohmmeter between MAF sensors connector terminal 3 and ground.

The ohmmeter should read approx. 11 k ohms.

If value OK:
^ Check load signal. Proceed to CHECK LOAD SIGNAL section below.

If ohmmeter reads approx. 0 ohms:
^ Check lead between ECM # 7 and MAF sensor terminal 3 for short circuit to ground.

If ohmmeter reads infinite resistance:
^ Check ECM connector. Proceed to CHECK ECM CONNECTOR section below.




CHECK ECM CONNECTOR
- Ignition off.
- Check ECM connector for contact resistance and oxidation.
- ECM connected.



- Connect an ohmmeter between MAF sensors connector terminal 3 and ground.

The ohmmeter should read approx. 11 k ohms.

If value OK:
^ Source of DTC is bad contact in ECM connector.

If ohmmeter reads infinite resistance:
^ Check lead between MAF sensor terminal 3 and ECM # 7 for break.

CHECK LOAD SIGNAL
- Ignition on.
- Erase DTC.
- Start and warm up engine.
- Gear selector: neutral, A/C: off.
- Power consumers such as engine coolant fan, heated rear window, etc.: off.
- Enter parameter list.



- Read off load signal.

Values should be 2.3 - 2.4 volts at idle.

If value OK:
^ Source of DTC is bad contact in MAF sensors and/or ECM connector. Check connectors for contact resistance and oxidation.

If value differs:
^ Test with new MAF sensor.

NOTE: Check in Diagnostic Test Mode (DTM) 1 for automatic transmission whether DTC for load signal is triggered.




INTERMITTENT FAULT, SIGNAL TOO HIGH
Check leads and terminals
- Check lead between MAF sensor terminal 3 and ECM # 7 for intermittent short circuit to live.
- Check lead between MAF sensor terminal 1 and ground for intermittent break.
- Check lead between MAF sensor terminal 2 and ECM # 26 for intermittent break.
- Check 55-pin connector in central relay unit (A3/E) terminal 13, MAF sensors and ECM connector for loose connection, as well as contact resistance and oxidation.




INTERMITTENT FAULT, SIGNAL TOO LOW
Check leads and terminals
- Check MAF sensors and ECM connector for loose connection, as well as contact resistance and oxidation.
- Check lead between MAF sensor terminal 3 and ECM # 7 for intermittent break, as well as intermittent short circuit to ground.
- Check lead between MAF sensor terminal 5 and ECM # 37 for intermittent break.

pro multis · About Operation CHARM