Signal Too Low. Permanent Fault

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 (A/C) pressure sensor connector terminal 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:
- Proceed to teset step below.





Checking for a Short-Circuit

The air conditioning (A/C) pressure sensor power cable is connected inside the engine control module (ECM) to the fuel tank pressure sensor, atmospheric pressure sensor and accelerometer power cables. If anything happens to any of these cables all four will be affected.

Check Cables Between:

- Accelerometer terminal 1 and engine control module (ECM) #B1.
- Air conditioning (A/C) pressure sensor terminal 3 and engine control module (ECM) #B29.
- Atmospheric pressure sensor terminal 1 and engine control module (ECM) #B29.
- Tank pressure sensor terminal 1 and engine control module (ECM) #B15.
- For a short-circuit to supply voltage.

Then proceed to Verification secion below.





Checking Signal Cable Resistance

- Ignition OFF.
- A/C pressure sensor disconnected.
- Connect an ohmmeter between air conditioning (A/C) pressure sensor connector 2 and ground.

The ohmmeter should read approx. 10K Ohms.

If reading is OK:
- Proceed to test step below.

If reading is incorrect:
- Check cable between A/C pressure sensor terminal 2 and engine control module (ECM) #B9 for a short- circuit to ground.
- Then proceed to Verification secion below.





Checking the Air Conditioning Pressure Sensor

- Ignition OFF.
- Connect air conditioning (A/C) pressure sensor.
- START the engine and idle it.
- A/C button ON.
- Blower fan ON.
- Go into scrolling value list.
- Read off air conditioning (A/C) pressure sensor signal.

Voltage should increase when the air conditioning (A/C) compressor starts.

If reading is OK:
- The diagnostic trouble code (DTC) has been caused by loose connections in the air conditioning (A/C) pressure sensor connector.
- Check connector for contact resistance, oxidation and remedy.
- Then proceed to Verification secion below.

If reading is incorrect:
- Try a new air conditioning (A/C) pressure sensor.
- Then proceed to Verification secion below.





Checking Power Cable Resistance To Ground

- Ignition OFF.
- Air conditioning (A/C) pressure sensor disconnected.
- Wait for approx. 150 seconds (cars with immobilizer 245 seconds).
- Connect an ohmmeter between air conditioning (A/C) pressure sensor connector 3 and ground.

The ohmmeter should read approx. 0.2K - 1.5K Ohms.

If value is Lower:
- Proceed to test step below.

If value is Higher:
- Proceed to Checking Engine Control Module Connector section below.





Checking Accelerometer

- Ignition OFF.
- Air conditioning (A/C) pressure sensor disconnected.
- Disconnect accelerometer.
- Connect an ohmmeter between air conditioning (A/C) pressure sensor connector 3 and ground.

The ohmmeter should read approx. 0.2K - 1.5K Ohms.

If reading is OK:
- Try a new accelerometer.
- Then proceed to Verification section below.

If reading is incorrect:
- Proceed to test step below.





Checking Atmospheric Pressure Sensor

- Ignition OFF.
- Air conditioning (A/C) pressure sensor and accelerometer disconnected.
- Disconnect atmospheric pressure sensor.
- Connect an ohmmeter between air conditioning (A/C) pressure sensor connector 3 and ground.

The ohmmeter should read approx. 0.2K - 1.5K Ohms.

If reading is OK:
- Try a new atmospheric pressure sensor.
- Then proceed to Verification section below.

If reading is incorrect:
- Proceed to test step below.





Checking Fuel Tank Pressure Sensor

- Ignition OFF.
- Air conditioning (A/C) pressure sensor, accelerometer and atmospheric pressure sensor disconnected.
- Disconnect fuel tank pressure sensor.
- Connect an ohmmeter between air conditioning (A/C) pressure sensor connector 3 and ground.

The ohmmeter should read approx. 0.2K - 1.5K Ohms.

If reading is OK:
- Try a new fuel tank pressure sensor.
- Then proceed to Verification section below.

If reading is incorrect:
- Proceed to test step below.





Checking for a Short-Circuit

The air conditioning (A/C) pressure sensor power cable is connected inside the engine control module (ECM) to the fuel tank pressure sensor, atmospheric pressure sensor and accelerometer power cables. If anything happens to any of these cables all four will be affected.

Check Cables Between:

- Accelerometer terminal 1 and engine control module (ECM) #B1.
- Air conditioning (A/C) pressure sensor terminal 3 and engine control module (ECM) #B29.
- Atmospheric pressure sensor terminal 1 and engine control module (ECM) #B29.
- Tank pressure sensor terminal 1 and engine control module (ECM) #B15.
- For a short-circuit to ground.

Then proceed to Verification section below.





Checking Engine Control Module Connector

- Ignition OFF.
- Air conditioning (A/C) pressure sensor disconnected.
- Check engine control module (ECM) connector for contact resistance, oxidation and remedy.
- Engine control module (ECM) connected.
- Connect an ohmmeter between air conditioning (A/C) pressure sensor connector 3 and ground.

The ohmmeter should read approx. 0.2K - 1.5K Ohms.

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

If reading is incorrect:
- Check cable between air conditioning (A/C) pressure sensor terminal 3 and engine control module (ECM) #B29 for an open-circuit.





Verification

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

- Ignition OFF.
- Air conditioning (A/C) pressure sensor and engine control module (ECM) connected.
- START the engine and idle it.
- A/C button ON.
- Blower fan ON.
- Wait until the air conditioning (A/C) compressor has started.
- Read off diagnostic trouble codes (DTCs).

If EFI-225 is stored it should have Intermittent Fault Status.

Alternative Intermittent:
- Fault corrected.

Alternative Permanent:
- Proceed to test step below.

Fault-Tracing Information

- The verification result shows that the fault persists.
- Do you want to exit fault-tracing?

Yes:
- Fault not corrected

No:
- Return to Checking Power Cable section above.