DTC 5-2-1

5-2-1 FRONT HEATED OXYGEN SENSOR, PREHEATING

Preconditions for DTC
^ Monitoring of the Heated Oxygen Sensor (HO2S) heating circuit begins approx. 3 minutes after the HO2S preheating sequence starts.
^ If the ECM registers excessive or insufficient current in the heating circuit, DTC 5-2-1 or 5-2-2 will be set.

Substitute value
^ Fuel trim is inhibited.

Fault sources
^ Signal too high:
- Signal lead short circuited to voltage supply.
- Defective HO2S.

^ Signal too low:
- Signal lead short circuited to ground.
- Break in signal or voltage lead.
- Contact resistance in connectors.
- Defective HO2S.

Fault symptoms
^ None.

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 HO2S (front HO2S: black connector; rear HO2S: grey connector).
^ Switch Ignition ON.
^ Connect a voltmeter between HO2S connector 2 (to ECM) and ground.

The voltmeter should show approx. 0 Volts.

If reading is OK:
- Test with a new HO2S.
If reading is incorrect:
- Check the lead between HO2S connector 2 and ECM A14 for signs of short circuiting to voltage supply.

PERMANENT FAULT, SIGNAL TOO LOW





Checking the Voltage Lead
^ Switch Ignition OFF.
^ Disconnect the HO2S (front HO2S: black connector; rear HO2S: grey connector).
^ Switch Ignition ON.
^ Connect a voltmeter between HO2S connector 1 (for main relay 2/32) and ground.

The voltmeter should show battery voltage.

If reading is OK:
- Check the signal lead.
If reading is incorrect:
- Check the lead between HO2S connector 1 and main relay (2/32) connector 3 for signs of a break.





Checking the Signal Lead
^ Switch Ignition ON.
^ HO2S disconnected.
^ Connect a voltmeter between the HO2S connector 2 (to control module) and ground.

The voltmeter should show approx. 0 Volts.

If the reading is OK:
- Check the signal lead's resistance to ground.
If the value differs:
- Check the lead between the HO2S connector 2 and control module A14 for signs of short circuiting to voltage supply.





Checking the Signal Lead's Resistance to Ground
^ Switch Ignition OFF.
^ Wait for about 150 seconds.
^ HO2S disconnected.
^ Disconnect the ECM.
^ Connect an ohmmeter between HO2S connector 2 (to ECM) and ground.

The ohmmeter should show infinite resistance.

If reading is OK:
- Check the signal lead's resistance.
If reading is incorrect:
- Check the lead between the HO2S connector 2 and ECM A14 for signs of short circuiting to ground.





Checking the Signal Lead's Resistance
^ Switch Ignition OFF.
^ HO2S disconnected.
^ ECM disconnected.
^ Connect the break-out box and check the ground connections.





^ Connect an ohmmeter between HO2S connector 2 (to ECM) and the break-out box connection #14 (ECM A14).

The ohmmeter should show approx. 0 ohms.

If reading is OK:
- Check the HO2S.
If reading is incorrect:
- Check the lead between HO2S connector 2 and ECM A14 for signs of a break.





Checking the HO2S
^ Switch Ignition OFF.
^ Connect the HO2S.
^ ECM disconnected.
^ Connect an ohmmeter between break-out box connector #27 (ECM A27) and #14 (ECM A14).

The ohmmeter should show 1.5 - 13 ohms.

If reading is OK:
- The source of the DTC is poor contact in the ECM's and/or the HO2S's connector.
- Rectify the connectors with regard to contact resistance and oxidation.
If reading is incorrect:
- Test with a new HO2S.

INTERMITTENT FAULT, SIGNAL TOO HIGH





Checking the leads and connectors
^ Check the lead between the HO2S connector 2 and ECM A14 for signs of intermittent short circuiting to voltage supply.

INTERMITTENT FAULT, SIGNAL TOO LOW

Checking the Leads and Connectors
^ Check the lead between HO2S connector 1 and main relay (2/32) connector 3 for signs of an intermittent break.
^ Check the lead between HO2S connector 2 and ECM A14 for signs of intermittent short circuiting to ground as well as an intermittent break.
^ Check the HO2S's and ECM's connectors for signs of loose connection, contact resistance and oxidation.