DTC 1-2-3

ED. Diagnostic trouble code (DTC) 1-2-3 MFI LH 2.4

* 1-2-3 Engine coolant temperature (ECT) signal absent or faulty



DTC conditions
If the signal from the ECT sensor corresponds to a temperature below -40°C (-40°F) or over 120°C (240°F) a DTC is logged.
The control module assumes that the coolant temperature is 20°C (68°F) when the engine is started and 90°C (1 94°F) otherwise (limp home) so that the car can be driven.

Causes of fault:
Break in or grounding of wiring, connections or a component.
Contact resistance in connections.
Poor signal GND connection.

Fault symptoms:
Difficult to start the engine when cold.

ED1




Resetting diagnostic trouble codes (DTCs)
- Read and delete the DTCs.
- Start the engine and let it run for about a minute.

If the DTC recurs:
^ Check the reference voltage ED2.

If the DTC does not recur:
Intermittent fault.
^ Check the ECT sensor connections and wiring for loose contacts in accordance with NA5 and clean the ECT sensor connector and treat it for corrosion in accordance with NA7. NA. Checking the Wiring

ED2




Checking the reference voltage
- Ignition on.
- Disconnect the sensor.
Connect a voltmeter between terminal 1 on the connector and GND.
The voltmeter should read about 5 V.

If this value is 0K:
^ Checking the ECT sensor resistance ED3.

If the reading is 0 V:
^ Connect the test box ED4.

ED3




Checking the engine coolant temperature (ECT) sensor resistance
- Ignition off
- Sensor disconnected.
Connect an ohmmeter between terminal 1 on the sensor and GND.




The readings from the ohmmeter should coincide with this graph.

If the value Is OK:
^ Connect the test box ED4.

If the reading deviates:
^ Try using a new sensor.

ED4




Connecting the test box
Connect the test box and check the GND points in accordance with P1-P2. P. Test Box, Signal Description
^ Continue with Checking the resistance to GND ED5.

ED5




Checking the resistance to GND
- Ignition off.
- Sensor disconnected.
Connect an ohmmeter between #13 and #5 (GND).
The ohmmeter should read infinite resistance.

If this value is OK:
^ Check the resistance of the sensor and wiring ED6.

If the reading is incorrect:
^ Check the wiring for grounding In accordance with NA3. NA. Checking the Wiring

ED6




Checking the resistance of the sensor and wiring
- Ignition off.
- Connect the sensor.
Connect an ohmmeter between #13 and #5 (GND).




The readings from the ohmmeter should coincide with this graph.

If the value is OK:
^ Clean the ECT sensor connector and treat it for corrosion in accordance with NA7. NA. Checking the Wiring
^ Continue with Checking the signal ED7.

If the reading is incorrect:
^ Check the wiring for breaks and contact resistance in accordance with NA2 and NA6 and clean the ECT sensor connector and treat it for corrosion in accordance with NA7. NA. Checking the Wiring

ED7




Checking the signal
- Connect the control module to the test box.
- Install fuse 1 (or 31).
- Ignition on.
Connect a voltmeter between #13 and #5 (GND).




The voltmeter readings should coincide with the graph.

Note: Readings are not stable on the 1992 model onwards.

If readings OK:
Intermittent fault.
^ Check the connections for loose contacts.

If the reading is 0 V:
^ Try using a new control module.

If the reading is incorrect:
^ Check the connections for contact resistance in accordance with NA6. NA. Checking the Wiring