DTC 2-1-2

EH. Diagnostic trouble code (DTC) 2-1-2 MFI LH 2.4

2-1-2 Heated oxygen sensor (HO2S) signal absent or faulty

If DTC 2-1-2 is logged at the same time as other DTCs, the first code to be presented by the OBD system should be remedied first. The following DTCs are regarded as secondary faults.




DTC conditions:
If the signal is absent the control module cannot handle HO2S control. A DTC is logged if the signal is faulty (over 1.1 V) or absent (0.5 V), 3 minutes after engine temperature has exceeded 80°C (1 76°F).

Causes of fault:
Breaks, short circuits in the HO2S wiring. Contact resistance in connections. No pre-heating of the HO2S.

Fault symptoms:
High fuel consumption, can cause driving problems.

EH1




Checking the signal from the heated oxygen sensor (HO2S)
- Start and warm up the engine.
Connect a voltmeter between terminal 1(1-pole connector at the firewall) and GND.
The voltmeter reading should fluctuate between 0.1-0.9 V.

If the reading is 0K:
Intermittent fault.
^ Check the wiring for loose contacts in accordance with NA5. NA. Checking the Wiring
If no faults are detected, connect the ST.

If the reading is constant approx. 0.5 V:
^ Check the HO2S pre-heater EH6.

If the reading is constant approx 0 V:
^ Check the HO2S reference voltage EH2.

If the reading is constant over 1.0 V:
^ Check the HO2S reference voltage EH2.

EH2




Checking the heated oxygen sensor (HO2S) reference voltage
- Ignition on.
- Disconnect the HO2S 1-pole connector.
Connect a voltmeter between the 1-pole connector (by the control module) and GND.
The voltmeter should read approx. 0.5 V.

If this value is OK:
^ Check the MAF sensor GND point EH8.

If the reading is approx 0 V:
^ Connect the test box.

If the reading is over 1 volt:
^ Check the wiring between MFI #24 and the HO2S for short circuits in accordance with NA4. NA. Checking the Wiring

When the fault has been remedied:
^ Check the signal from the HO2S in accordance with EH1.

EH3




Connecting the test box
Connect the test box to MFI and check the GND points in accordance with P1-P2. P. Test Box, Signal Description
^ Continue with Checking the signal wiling EH4.

EH4




Checking signal wiring
- Ignition off
Connect an ohmmeter between #24 and #5
The ohmmeter should read infinite resistance.

If this reading is OK:
^ Check the resistance in the wiling EH5.

If the reading is 0 ohms.
^ Check the wiling to control module #24 for grounding in accordance with NA3. NA. Checking the Wiring

EH5




Checking the resistance in the wiring
Connect an ohmmeter between #24 and the 1-pole connector at the firewall (by the control module).
The ohmmeter should read 0 ohms.

If this value is OK:
^ Try using a new control module.

If resistance is infinite:
^ Check the wiring to control module #24 for breaks in accordance with NA2. NA. Checking the Wiring

EH6




Checking oxygen sensor (HO2S) preheating
- Engine running.
Connect a voltmeter between terminal 2 and ground in the 2-pin connector.
The voltmeter should indicate battery voltage.

If this value is OK:
^ Check the GND point EH7.

If the reading is approx. 0 V:
^ Check the wiring between fuse 11 (740, 940,780) or the fuel injection relay (760, 960) and the connector for breaks in accordance with NA2. NA. Checking the Wiring

EH7




Checking the GND point
- Engine running.
Connect a voltmeter between terminals 1 and 2 in the HO2S 2-pole connector.
The voltmeter should read approx 12 V.

If this value is OK:
^ Check the MAF sensor GND point EH8.

If the reading is incorrect:
^ Check the wiring to the GND point for breaks in accordance with NA2. NA. Checking the Wiring

EH8




Checking the mass air flow (MAF) sensor GND point
- Ignition off.
- Disconnect the connector from the MAF sensor.
Connect an ohmmeter between terminal 1 in the MAF sensor connector and GND.
The ohmmeter should read 0 ohms.

If this value is OK:
^ Check the MAF sensor signal EH9.

If the reading is incorrect:
^ Check the wiring to the GND point for contact resistance in the intake manifold GND point in accordance with NA6. NA. Checking the Wiring

EH9




Checking the mass air flow (MAF) sensor signal
- Clean the MAF sensor connector and treat it for corrosion in accordance with NA7. NA. Checking the Wiring
- Install the connector.
- Start the engine.
Connect a voltmeter between 3 (on the back of the MAF sensor connector) and GND.
The voltmeter should read approx. 2.3 V.

If this value is OK:
^ Try using a new HO2S.

If the reading is incorrect:
^ Replace the MAF sensor and repeat the readings In accordance with EH1.