Signal Too High. Permanent Fault

Checking Power Cable
- Ignition OFF.
- Disconnect CO potentiometer.
- Ignition ON.
- Connect a voltmeter between CO potentiometer connector terminal 3 and ground.
- The voltmeter should read 5 Volts.

If reading is OK:
^ Proceed to: Checking Ground Lead section below.

If value is lower
^ Proceed to: Checking Power Cable Resistance to Ground section below.

If value is higher:
^ The CO potentiometer power cable is connected to the air conditioning (A/C) pressure sensor power cable inside the engine control module (ECM). If anything happens to either of these cables both will be affected.
^ Air conditioning pressure sensor wiring is pre-routed, even on cars without air conditioning, and should always be checked. Check cables between: CO potentiometer terminal 3 and engine control module # B1 air conditioning pressure sensor terminal 3 and engine control module # B29 for a short-circuit to supply voltage.
^ Proceed to: Verification section below.





Checking Ground Lead
- Ignition OFF.
- CO potentiometer disconnected.
- Connect an ohmmeter between CO potentiometer connector terminal 1 and ground.
- The ohmmeter should read approx. 0 ohms.

If reading is OK:
^ Proceed to: Checking the Signal Cable section below.

If reading is incorrect:
^ Proceed to: Checking ECM Connector section below.




Checking ECM Connector
- Ignition OFF.
- CO potentiometer disconnected.
- Check engine control module connector for contact resistance and oxidation and remedy.
- Engine control module connected.
- Connect an ohmmeter between CO potentiometer connector terminal 1 and ground.
- The ohmmeter should read approx. 0 ohms.

If reading is OK:
^ The cause of the diagnostic trouble code (DTC) has been loose connections in the engine control module connector.
^ Proceed to: Verification section below.

If reading is incorrect:
^ Check cable between CO potentiometer terminal 1 and engine control module # B28 for an open-circuit.
^ Proceed to: Verification section below.





Checking the Signal Cable
- Ignition ON.
- CO potentiometer disconnected.
- Connect a voltmeter between CO potentiometer connector terminal 2 and ground.
- The voltmeter should read approx. 5 Volts.

If reading is OK:
^ Proceed to: Checking CO Potentiometer section below.

If value is lower:
^ Proceed to: Checking ECM Connector section below.

If value is higher:
^ Check cable between CO potentiometer terminal 2 and engine control module # B32 for a short-circuit to supply voltage.
^ Proceed to: Verification section below.





Checking ECM Connector
- Ignition OFF.
- CO potentiometer disconnected.
- Check engine control module connector for contact resistance and oxidation and remedy.
- Engine control module connected.
- Ignition ON.
- Connect a voltmeter between CO potentiometer connector terminal 2 and ground.
- The voltmeter should read approx. 5 Volts.

If reading is OK:
^ The cause of the diagnostic trouble code has been loose connections in the engine control module connector.
^ Proceed to: Verification section below.

If reading is incorrect:
^ Check cable between CO potentiometer terminal 2 and engine control module # B32 for an open-circuit.
^ Proceed to: Verification section below.





Checking CO Potentiometer
- Remove seal.
- Drill two holes in the plug. 2 mm (0.079 in) drill.
- Pull out plug with circlip ring pliers.
- Connect CO potentiometer.
- Start the engine and idle it.
- Go into scrolling values. Read off CO potentiometer value.
- Turn adjustment screw clockwise to lower voltage.
- It should be possible to adjust voltage between 0 Volts and 5 Volts.

If reading is OK:
^ Adjust CO.
^ Proceed to: Verification section below.

If reading is incorrect:
^ Try a new CO potentiometer.
^ Proceed to: Verification section below.





Checking Power Cable Resistance to Ground
- Ignition OFF.
- CO potentiometer disconnected.
- Wait approx. 150 seconds.
- Connect an ohmmeter between CO potentiometer connector terminal 3 and ground.
- Does the ohmmeter read approx. 0 ohms ?

Yes:
^ Proceed to: Check section below.

No:
^ Proceed to: Checking the A/C Pressure Sensor section below.

Check
- Car variant?

Alternative A/C:
^ The car has air conditioning (A/C).
^ Proceed to: Checking the A/C Pressure Sensor section below.

Alternative Ej A/C:
^ The CO potentiometer power cable is connected to the air conditioning pressure sensor power cable inside the engine control module. If anything happens to either of these cables both will be affected.
^ Air conditioning pressure sensor wiring is pre-routed, even on cars without air conditioning, and should always be checked.
^ Check cables between: CO potentiometer terminal 3 and engine control module # B1 air conditioning pressure sensor terminal 3 and engine control module # B29 for a short-circuit to supply voltage.
^ Proceed to: Verification section below.





Checking ECM Connector
- Ignition OFF.
- CO potentiometer disconnected.
- Check engine control module connector for contact resistance and oxidation.
- Engine control module connected.
- Connect an ohmmeter between CO potentiometer connector terminal 3 and ground.
- The ohmmeter should read approx. 0.2 - 1.5 k ohms.

If reading is OK:
^ The cause of the diagnostic trouble code has been loose connections in the engine control module connector.
^ Proceed to: Verification section below.

If reading is incorrect:
^ Check cable between CO potentiometer terminal 3 and engine control module # B1 for an open-circuit.
^ Proceed to: Verification section below.





Checking the A/C Pressure Sensor
- Ignition OFF.
- CO potentiometer disconnected.
- Disconnect the air conditioning pressure sensor.
- Connect an ohmmeter between CO potentiometer connector terminal 3 and ground.
- The ohmmeter should read 0.2 - 1.5 k ohms.

If reading is OK:
^ Try a new air conditioning pressure sensor.
^ Proceed to: Verification section below.

If reading is incorrect:
^ The CO potentiometer power cable is connected to the air conditioning pressure sensor power cable inside the engine control module. If anything happens to either of these cables both will be affected.
^ Check cables between: CO potentiometer terminal 3 and engine control module # B1 air conditioning pressure sensor terminal 3 and engine control module # B29 for a short-circuit to supply voltage.
^ Proceed to: Verification section below.





Verification
After carrying out the repair, check that the fault has been remedied as follows:

- CO potentiometer, air conditioning pressure sensor and engine control module connected.
- Erase diagnostic trouble code.
- Start the engine and idle it, wait 1 minute.
- Diagnostic trouble code should not recur.

If reading is OK:
^ Fault corrected.

If reading is incorrect:
^ Proceed to: Fault-tracing Information section below.

Fault-tracing Information
The verification result shows that the fault persists.

- Do you want to exit fault-tracing?

Yes:
^ Fault not corrected.

No:
^ Proceed to: Checking Power Cable section above.