FREE REPAIR MANUALS & LABOR GUIDES 1982-2013 Vehicles
Courtesy of Operation CHARM: Car repair manuals for everyone.
Home >> Volvo >> 1996 >> 850 Turbo L5-2.3L Turbo VIN 57 B5234FT >> Repair and Diagnosis >> A L L Diagnostic Trouble Codes ( DTC ) >> Testing and Inspection >> Manufacturer Code Charts >> EFI / DTC Codes (Engine Control System) >> DTC 2-1-2

DTC 2-1-2

2-1-2 FRONT HEATED OXYGEN SENSOR SIGNAL

Preconditions for DTC
^ One of the preconditions for fuel trim to begin is that the Front Heated Oxygen Sensor (HO2S) must be ready to regulate, i.e. it should be at operational temperature and have the correct output voltage. Monitoring of the HO2S begins about 3 minutes after HO2S preheating starts. If there is a fault with the front or rear HO2S or their leads, so that the output voltage from the front HO2S deviates from the permitted value, DTC 2-1-2 will be set.

Substitute values
^ Fuel trim is inhibited.
^ Three-Way Converter (TWC) diagnosis inhibited.

Fault sources
^ Signal too high:
- Signal lead (+) short circuited to voltage supply.
- Signal lead (-) short circuited to voltage supply.
- Defective front HO2S.
- Defective rear HO2S.

^ Signal too low:
- Signal lead (+) short circuited to ground.
- Signal lead (-) short circuited to ground.
- Defective front HO2S.

^ Signal absent:
- Break in signal lead (-).
- Signal lead (+) short circuited to ground.
- Signal lead (-) short circuited to ground.
- Defective front HO2S.
- Defective rear HO2S.

^ Faulty signal:
- Signal lead (+) short circuited to signal lead (-).
- Defective front HO2S.

Fault symptoms
^ None.

TESTING PROCEDURE





Other DTCs
^ Check for other DTCs.

If DTC 5-2-1 is stored:
- See Testing By Trouble Code / DTC 5-2-1 Front Heated Oxygen Sensor Preheating.
If DTC 5-2-1 is not stored:
- Check Status message.





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: Permanent fault, signal absent:
- Proceed to: PERMANENT FAULT, SIGNAL ABSENT section below.
If Status message is: Permanent fault, faulty signal:
- Proceed to: PERMANENT FAULT, FAULTY SIGNAL 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.
If Status message is: Intermittent fault, signal absent:
- Proceed to: INTERMITTENT FAULT, SIGNAL ABSENT section below.
If Status message is: Intermittent fault, faulty signal:
- Proceed to: INTERMITTENT FAULT, FAULTY SIGNAL section below.

PERMANENT FAULT, SIGNAL TOO HIGH





Checking Signal Lead (-), Front HO2S
^ Connect measuring instrument and check the ground connections.
^ Connect the ECM.
^ Switch Ignition ON.
^ Connect a voltmeter between connectors #33 (A33) and #42 (A42) on the measuring instrument.

The voltmeter should show approx. 0.7 Volts.

If reading is OK:
- Check the signal lead (+), front HO2S.
If reading is incorrect:
- Check the front HO2S.





Checking the Front HO2S
^ Switch Ignition OFF.
^ Disconnect the front HO2S (black connector).
^ Switch Ignition ON.
^ Connect a voltmeter between connectors #33 (A33) and #42 (A42) on the measuring instrument.

The voltmeter should show approx. 0.7 Volts.

If reading is OK:
- Test with a new front HO2S.
If reading is incorrect:
- Check the rear HO2S.





Checking the Rear HO2S
^ Switch Ignition OFF.
^ Front HO2S disconnected.
^ Disconnect the rear HO2S (gray connector).
^ Switch Ignition ON.
^ Connect a voltmeter between connectors #33 (A33) and #42 (A42) on the measuring instrument.

The voltmeter should show approx. 0.7 Volts.

If reading is OK:
- Test with a new rear HO2S.
If reading is incorrect:
- Check the lead between the front HO2S connector 3 and ECM A33 and the lead between the rear HO2S connector 3 and ECM A19 for signs of short circuiting to voltage supply.





Checking Signal Lead (+), Front HO2S
^ Switch Ignition ON.
^ Connect a voltmeter between connectors #32 (A32) and #42 (A42) on the measuring instrument.

The voltmeter should show approx. 1.2 Volts.

If reading is OK:
- Check the signal lead (+), rear HO2S.
If reading is incorrect:
- Check the front HO2S.





Checking the Front HO2S
^ Switch Ignition OFF.
^ Disconnect the front HO2S (black connector).
^ Switch Ignition ON.
^ Connect a voltmeter between connectors #32 (A32) and #42 (A42) on the measuring instrument.

The voltmeter should show approx. 1.2 Volts.

It reading is OK:
- Test with a new front HO2S.
If reading is incorrect:
- Check the lead between the front HO2S connector 4 and ECM A32 for signs of short circuiting to voltage supply.





Checking the Signal Lead (+), Rear HO2S
^ Switch Ignition OFF.
^ Disconnect the rear HO2S (gray connector).
^ Switch Ignition ON.
^ Connect a voltmeter between connectors #34 (A34) and #42 (A42) on the measuring instrument.

The voltmeter should show approx. 0 Volts.

It reading is OK:
- Test with a new rear HO2S.
It reading is incorrect:
- Check the lead between the rear HO2S connector 4 and ECM A34 for signs of short circuiting to voltage supply.

PERMANENT FAULT, SIGNAL TOO LOW





Checking the Signal Lead (-), Front HO2S
^ Connect the measuring instrument and check the ground connections.
^ Connect the ECM.
^ Switch Ignition ON.
^ Connect a voltmeter between connectors #33 (A33) and #42 (A42) on the measuring instrument.

The voltmeter shows approx. 0.7 Volts.

It reading is OK:
- Check the signal lead (+), front HO2S.
If reading is incorrect:
- Check the front HO2S.





Checking the Front HO2S
^ Switch Ignition OFF.
^ Disconnect the front HO2S (black connector).
^ Switch Ignition ON.
^ Connect a voltmeter between connectors #33 (A33) and #42 (A42) on the measuring instrument.

The voltmeter should show approx. 0.7 Volts.

If reading is OK:
- Test with a new front HO2S.
If reading is incorrect:
- Check the rear HO2S.





Checking the Rear HO2S
^ Switch Ignition OFF.
^ Front HO2S disconnected.
^ Disconnect the rear HO2S (gray connector).
^ Switch Ignition ON.
^ Connect a voltmeter between connectors #33 (A33) and #42 (A42) on the measuring instrument.

The voltmeter shows approx. 0.7 Volts.

If reading is OK:
- Test with a new rear HO2S.
If reading is incorrect:
- Check the lead between the front HO2S connector 3 and ECM A33 and the lead between the rear HO2S connector 3 and ECM A19 for signs of short circuiting to ground.





Checking the Signal Lead (+), Front HO2S
^ Switch Ignition OFF.
^ Disconnect the front HO2S (black connector).
^ Switch Ignition ON.
^ Connect a voltmeter between connectors #32 (A32) and #42 (A42) on the measuring instrument.

The voltmeter should show approx. 1.2 Volts.

If reading is OK:
- Test with a new front HO2S.
If reading is incorrect:
- Check the lead between the front HO2S connector 4 and ECM A32 for signs of short circuiting to ground.

PERMANENT FAULT, SIGNAL ABSENT





Checking the Signal Lead (+), Front HO2S
^ Switch Ignition OFF.
^ Wait for approx. 150 seconds.
^ Disconnect the front HO2S (black connector).
^ Connect an ohmmeter between the HO2S connector 4 (to control module) and ground.

The ohmmeter should show approx. 50K ohms.

If reading is OK:
- Check the signal lead (-), front HO2S.
If the ohmmeter shows infinite resistance:
- Check the control module connector.
If the ohmmeter shows approx. 0 ohms:
- Check the lead between front HO2S connector 4 and ECM A32 for signs of short circuiting to ground.





Checking the ECM's Connector
^ Switch Ignition OFF.
^ Front HO2S disconnected.
^ Rectify the ECM's connector with regard to contact resistance and oxidation.





^ ECM connected.
^ Connect an ohmmeter between the HO2S connector 4 (to ECM) and ground.

The ohmmeter should show approx. 50K ohms.

If reading is OK:
- The cause of the DTC is poor contact in the ECM's connector.
If reading is incorrect:
- Check the lead between front HO2S connector 4 and ECM A32 for signs of a break.





Checking the Signal Lead (-), Front HO2S
^ Switch Ignition OFF.
^ Front HO2S disconnected.
^ Connect an ohmmeter between the HO2S connector 3 (to ECM) and ground.

The ohmmeter should show approx. 200 ohms.

If reading is OK:
- Check the signal, front HO2S.
If the ohmmeter shows infinite resistance:
- Check the ECM's connector.
If the ohmmeter shows approx. 0 ohms:
- Check the rear HO2S.





Checking the ECM's Connector
^ Switch Ignition OFF.
^ Front HO2S disconnected.
^ Rectify the ECM's connector with regard to contact resistance and oxidation.





^ ECM connected.
^ Connect an ohmmeter between the HO2S connector 3 (to ECM) and ground.

The ohmmeter should show approx. 200 ohms.

If reading is OK:
- The source of the DTC is poor contact in the ECM connector.
If reading is incorrect:
- Check the lead between front HO2S connector 3 and ECM A33 for signs of a break.





Checking the Rear HO2S
^ Switch Ignition OFF.
^ Front HO2S disconnected.
^ Disconnect the rear HO2S (gray connector).
^ Connect an ohmmeter between the front HO2S connector 3 (to ECM) and ground.

The ohmmeter should show approx. 200 ohms.

If reading is OK:
- Test with a new rear HO2S.
If reading is incorrect:
- Check the lead between front HO2S connector 3 and ECM A33 and the lead between the rear HO2S connector 3 and ECM A19 for signs of short circuiting to ground.





Checking the Signal, Front HO2S
^ Switch Ignition OFF.
^ Connect the front HO2S.
^ START the engine and let it run at idling speed.
^ Look up the DTC parameter.
^ Read off the value for the front HO2S.

The signal should have shifted from its middle setting (0.45 V) and begun to swing between 0.1 - 0.9 Volts within a couple of minutes.

If reading is OK:
- The cause of the DTC is poor contact in the front HO2S connector.
- Check that the connector tabs are not damaged.
If reading is incorrect:
- Test with a new front HO2S.

NOTE: Rust-removal spray and grease may not be used on the HO2S connector.

PERMANENT FAULT, FAULTY SIGNAL





Checking the Front HO2S
^ Switch Ignition OFF.
^ Wait for approx. 150 seconds.
^ Disconnect the front HO2S (black connector).
^ Connect an ohmmeter between HO2S connector 3 and 4 (on HO2S).

The ohmmeter should show 50 ohms - infinite resistance.

If reading is OK:
- Check the lead between front HO2S connector 4 and ECM A32 for short circuiting in the lead between the front HO2S connector 3 and ECM A33.
If reading is incorrect:
- Test with a new front HO2S.





INTERMITTENT FAULT, SIGNAL TOO HIGH

Checking the Leads And Connections
^ Check the lead between front HO2S connector 4 and ECM A32 for signs of intermittent short circuiting to voltage supply.
^ Check the lead between front HO2S connector 3 and ECM A33 and the lead between the rear HO2S connector 3 and ECM A19 for signs of intermittent short circuiting to voltage.
^ Check the lead between rear HO2S connector 4 and ECM A34 for signs of intermittent short circuiting to voltage supply.

INTERMITTENT FAULT, SIGNAL TOO LOW

Checking the Leads And Connections
^ Check the lead between front HO2S connector 4 and ECM A32 for signs of intermittent short circuiting to ground.
^ Check the lead between front HO2S connector 3 and ECM A33 and the lead between the rear HO2S connector 3 and ECM A19 for signs of intermittent short circuiting to ground.

INTERMITTENT FAULT, SIGNAL ABSENT.

Checking the Leads And Connections.

NOTE: Rust-removal spray and grease may not be used on the HO2S connector.

^ Check the lead between front HO2S connector 4 and ECM A32 for signs of an intermittent break.
^ Check the lead between front HO2S connector 3 and ECM A33 for signs of an intermittent break.
^ Check the front HO2S and ECM connectors for signs of loose connection.
^ Check the lead between front HO2S connector 4 and ECM A32 for signs of intermittent short circuiting to ground.
^ Check the lead between front HO2S connector 3 and ECM A33 and the lead between the rear HO2S connector 3 and ECM A19 for signs of intermittent short circuiting to ground.

INTERMITTENT FAULT, FAULTY SIGNAL





Checking the Leads
^ Check the lead between the front HO2S connector 4 and ECM A32 for intermittent short circuiting to the lead between the front HO2S connector 3 and ECM A33.









pro multis Credits:Operation CHARM About Operation CHARM