DTC 2-4-5

2-4-5 IDLE AIR CONTROL VALVE SIGNAL CLOSING

Preconditions for DTC
^ If the ECM registers a fault on the line from the Idle Air Control (IAC) Valve's closing coil, DTC is set at 2-4-5.

Substitute values
^ The idle air trim is inhibited.
^ The conditions for fuel shutoff are changed.
^ Output signals to the coils will be regulated with a fixed value depending on the cause of the fault.

Fault sources
^ Signal too high:
- Signal lead short circuited to voltage.
- Opening coil and closing coil signal leads short circuited to each other.
- Defective IAC valve.

^ Signal too low:
- Break in signal lead.
- Break in voltage lead.
- Signal lead short circuited to ground or voltage.
- Defective IAC valve.
- Contact resistance in connections.

Fault symptoms
^ Low or high idling speed.
^ The engine may be difficult to start.

TESTING PROCEDURE





Status Message
^ Check current status message.

If Status message is: Permanent fault, signal too high:
- Proceed to: PERMANENT FAULT, SIGNAL TOO HIGH section below.
If Status message is: Permanent fault, signal too low:
- Proceed to: PERMANENT FAULT, SIGNAL TOO LOW section below.
If Status message is: Intermittent fault, signal too high:
- Proceed to: INTERMITTENT FAULT, SIGNAL TOO HIGH section below.
If Status message is: Intermittent fault, signal too low:
- Proceed to: INTERMITTENT FAULT, SIGNAL TOO LOW section below.

PERMANENT FAULT, SIGNAL TOO HIGH





Checking the Signal Lead
^ Switch Ignition OFF.
^ Disconnect the IAC valve.
^ Switch Ignition ON.
^ Connect a voltmeter between ground and the IAC valve connector 1.

The voltmeter should show less than 1 Volt.

If reading is OK:
- Check the signal lead resistance.
If reading is incorrect:
- Check the lead between the IAC valve's connector 1 and ECM A25 for signs of short circuiting to voltage.





Checking the Signal Lead Resistance
^ Switch Ignition OFF.
^ Wait for approx. 150 seconds.
^ IAC valve disconnected.
^ Connect an ohmmeter between AC valve connectors 1 and 3.

The ohmmeter shows 20 - 40K ohms.

If reading is OK:
- Test with a new IAC valve.
If the ohmmeter shows approx. 0 ohms:
- Check the lead between IAC valve connector 3 and ECM A11 for signs of short circuiting in the lead between the IAC valve connector 1 and ECM A25.
- If the IAC valve's signal leads are short circuited to each other, then both DTC 2-2-3 and 2-4-5 will be set.

PERMANENT FAULT, SIGNAL TOO LOW





Checking the Voltage Lead
^ Switch Ignition OFF.
^ Disconnect the IAC valve.
^ Switch Ignition ON.
^ Connect a voltmeter between IAC valve connector 2 and ground.

The voltmeter should show battery voltage.

If reading is OK:
- Check the signal lead's resistance to ground.
If reading is incorrect:
- Check the lead between the main relay (2/32) connector 3 and IAC valve connector 2 for signs of a break.
- If there is a break in the voltage lead, then both DTC 2-2-3 and 2-4-5 will be set.





Checking the Signal Lead's Resistance to Ground
^ Switch Ignition OFF.
^ Wait for approx. 150 seconds.
^ IAC valve disconnected.
^ Connect an ohmmeter between ground and the IAC valve's connector 1.

The ohmmeter should show 10 - 20K ohms.

If reading is OK:
- Check the IAC valve.
If the ohmmeter shows infinite resistance:
- Check the ECM's connector.
If the ohmmeter shows approx. 0 ohms:
- Check the lead between the IAC valve's connector 1 and ECM A25 for signs of short circuiting to ground.





Checking the ECM Connector
^ Switch Ignition OFF.
^ IAC valve disconnected.
^ Rectify the ECM's connector with regard to contact resistance and oxidation.





^ ECM connected.
^ Connect an ohmmeter between ground and the IAC valve connector 1.

The ohmmeter should show 10 - 20K ohms.

If reading is OK:
- The cause of the DTC is poor contact in the ECM connector.
If reading is incorrect:
- Check the lead between IAC valve connector 1 and ECM A25 for signs of a break.





Checking the IAC Valve
^ Switch Ignition OFF.
^ IAC valve disconnected.
^ Connect an ohmmeter between IAC valve connectors 1 and 2.
^ Read off the value.
^ Then connect the ohmmeter between IAC valve connectors 2 and 3.
^ Read off the values.

The ohmmeter should show 9 - 14 ohms at +20°C (680°F) in both cases.

If the values are OK:
- The cause of the DTC is poor contact in the IAC valve connector.
- Rectify the connector with regard to contact resistance and oxidation.
If the readings are incorrect:
- Test with a new IAC valve.

INTERMITTENT FAULT, SIGNAL TOO HIGH





Checking the Leads And Connections
^ Check the lead between IAC valve connector 1 and ECM A25 for signs of intermittent short circuiting to voltage.
^ Check the lead between IAC valve connector 1 and ECM A25 for signs of intermittent short circuiting to the shutting coil's signal lead.

INTERMITTENT FAULT, SIGNAL TOO LOW

Checking the Leads And Connections
^ Check the IAC valve's and ECM's connectors with regard to contact resistance and oxidation.
^ Check the lead between the main relay (2/32) connector 3 and IAC valve connector 2 for signs of an intermittent break.
^ Check the lead between IAC valve connector 1 and ECM A25 for signs of an intermittent break and intermittent short circuiting to ground.