Signal Too Low. Permanent Fault

Checking Power Cable
- Ignition OFF.
- Disconnect the air conditioning (A/C) pressure sensor.
- Ignition ON.
- Connect a voltmeter between air conditioning pressure sensor connector 3 and ground.
- The voltmeter should read 5 Volts.

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

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

If value is higher:
^ The air conditioning pressure sensor power cable is connected inside the engine control module (ECM) to the accelerometer (GS: CO-potentiometer) power cable. If anything happens to either of these cables both will be affected. They should always be checked.
^ Check cables between: Accelerometer (GS: CO-potentiometer) terminal 1 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 Signal Cable Resistance
- Ignition OFF.
- Air conditioning pressure sensor disconnected.
- Connect an ohmmeter between air conditioning pressure sensor connector 2 and ground.
- The ohmmeter should read approx. 10 k ohms.

If reading is OK:
^ Proceed to: Checking A/C Pressure Sensor section below.

If reading is incorrect:
^ Check cable between air conditioning pressure sensor terminal 2 and engine control module # B9 for a short-circuit to ground.
^ Proceed to: Verification section below.





Checking A/C Pressure Sensor
- Ignition OFF.
- Connect air conditioning pressure sensor.
- Start the engine and idle it.
- Air conditioning switch ON.
- Blower fan ON.
- Go into scrolling values.
- Read off air conditioning pressure sensor signal.
- Voltage should increase when the air conditioning compressor starts.

If reading is OK:
^ The cause of the diagnostic trouble code (DTC) has been loose connections in the air conditioning pressure sensor connector.
^ Check connector for contact resistance and oxidation and remedy.
^ Proceed to: Verification section below.

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





Checking Power Cable Resistance to Ground
- Ignition OFF.
- Air conditioning pressure sensor disconnected.
- Wait for approx. 150 seconds (cars with immobilizer 245 seconds).
- Connect an ohmmeter between air conditioning pressure sensor connector 3 and ground.
- The ohmmeter should read approx. 0.2 - 1.5 k ohms.

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

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





Checking Accelerometer
- Ignition OFF.
- Air conditioning pressure sensor disconnected.
- Disconnect one accelerometer (GS: CO-potentiometer).
- Connect an ohmmeter between air conditioning pressure sensor connector 3 and ground.
- The ohmmeter should read approx. 0.2 - 1.5 k ohms.

If reading is OK:
^ Try a new accelerometer.
^ Proceed to: Verification section below.

If reading is incorrect:
^ Proceed to: Checking Power Cables section below.





Checking Power Cables
- The air conditioning pressure sensor power cable is connected inside the engine control module to the accelerometer (GS: CO-potentiometer) power cable.
- If anything happens to either of these cables both will be affected. They should always be checked.
- Check cables between:

- Accelerometer (GS: CO-potentiometer) terminal 1 and engine control module # B1.
- Air conditioning pressure sensor terminal 3 and engine control module # B29 for a short-circuit to ground.

- Proceed to: Verification section below.





Checking ECM Connector
- Ignition OFF.
- Air conditioning pressure sensor disconnected.
- Check engine control module connector for contact resistance and oxidation and remedy.
- Engine control module connected.
- Connect an ohmmeter between air conditioning pressure sensor connector 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 air conditioning pressure sensor terminal 3 and engine control module # B29 for an open-circuit.
^ Proceed to: Verification section below.





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

- Ignition OFF.
- Air conditioning pressure sensor and engine control module connected.
- Start the engine and idle it.
- Air conditioning switch ON.
- Blower fan ON.
- Wait until the air conditioning compressor has started.
- Read off any diagnostic trouble codes.
- If EFI-225 is stored it should have intermittent fault status.

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.