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Home >> Volvo >> 1996 >> 850 GLT L5-2.4L VIN 55 B5254S >> Repair and Diagnosis >> A L L Diagnostic Trouble Codes ( DTC ) >> Testing and Inspection >> Manufacturer Code Charts >> EFI / DTC Codes (Engine Control System) >> Motronic 4.4 (MFI) >> DTC EFI-621 >> Signal Too Low. Permanent Fault

Signal Too Low. Permanent Fault





Checking Power Cable
- Ignition off.
- Wait for approx. 150 seconds (cars with immobilizer 245 seconds).
- Disconnect tank pressure sensor.
- Connect an ohmmeter between fuel tank pressure sensor connector terminal 1 (engine control module (ECM) side) and ground.
- The ohmmeter should read approx. 0.9K ohms.

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

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





Checking Power Cable Resistance
- Ignition off.
- Tank pressure sensor disconnected.
- Connect an ohmmeter between fuel tank pressure sensor connector terminal 1 (engine control module side) and ground.
- The ohmmeter should read infinite resistance.

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

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





Checking Connector 24/4
- Ignition off.
- Tank pressure sensor disconnected.
- Check connector 24/4 for contact resistance or oxidation and remedy.
- Assemble connector 24/4.
- Connect an ohmmeter between fuel tank pressure sensor connector terminal 1 (engine control module side) and ground.
- The ohmmeter should read approx. 0.9K ohms.

If reading is OK:
^ The diagnostic trouble code (DTC) has been caused by loose connections in connector 24/4.
^ Then proceed to Verification section below.

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





Checking Power Cable Between Connector 24/4 And Fuel Tank Pressure Sensor
- Ignition off.
- Tank pressure sensor disconnected.
- Disconnect connector 24/4.
- Connect an ohmmeter between connector 24/4 terminal E4 (engine control module side) and ground.
- The ohmmeter should read approx. 0.9K ohms.

If reading is OK:
^ Check cable between fuel tank pressure sensor terminal 1 and connector E4 for an open-circuit.
^ Then proceed to Verification section below.

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





Checking Connector 24/2
- Ignition off.
- Tank pressure sensor disconnected.
- Connector 24/4 disassembled.
- Check connector 24/2 for contact resistance or oxidation and remedy.
- Assemble connector 24/2.
- Connect an ohmmeter between connector 24/4 terminal E4 (engine control module (side) and ground.
- The ohmmeter should read approx. 0.9K ohms.

If reading is OK:
^ The diagnostic trouble code has been caused by loose connections in connector 24/2.
^ Then proceed to Verification section below.

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





Checking Power Cable Between Connector 24/4 And 24/2
- Ignition off.
- Disassemble connector 24/2.
- Connect an ohmmeter between connector 24/2 terminal C5 (engine control module side) and ground.
- The ohmmeter should read approx. 0.9K ohms.

If reading is OK:
^ Check cable between connector 24/2 terminal C5 and connector 24/4 terminal E4 for an open-circuit.
^ Then proceed to Verification section below.

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





Checking The Engine Control Module Connector
- Ignition off.
- Tank pressure sensor disconnected.
- Connector 24/4 disassembled.
- Check engine control module connector for contact resistance or oxidation and remedy.
- Connect engine control module.
- Connect an ohmmeter between connector 24/2 terminal C5 (engine control module side) and ground.
- The ohmmeter should read approx. 0.9K ohms.

If reading is OK:
^ The diagnostic trouble code was caused by loose connections in the engine control module connector.
^ Then proceed to Verification section below.

If reading is incorrect:
^ Check cable between connector 24/2 terminal C5 and engine control module # B15 for an open-circuit.
^ Then proceed to Verification section below.





Checking Power Cables
- Ignition off.
- Disassemble connector 24/4.
- Connect an ohmmeter between connector 24/4 terminal E4 (engine control module side) and ground.
- The ohmmeter should read approx. 0.9K ohms.

If reading is OK:
^ Check cable between connector 24/4 terminal E4 and fuel tank pressure sensor terminal 1 for a short-circuit to ground.
^ Then proceed to Verification section below.

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





Checking Cable Between 24/2 And 24/4
- Ignition off.
- Disassemble connector 24/2.
- Connect an ohmmeter between connector 24/2 terminal C5 (engine control module side) and ground.
- The ohmmeter should read approx. 0.9K ohms.

If reading is OK:
^ Check cable between connector 24/2 terminal C5 and connector 24/4 terminal E4 for a short-circuit to ground.
^ Then proceed to Verification section below.

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





Fault-tracing Information
- The fuel tank pressure sensor power cable is connected inside the engine control module to the accelerometer and A/C pressure sensor power cables. If anything happens to any of these cables all three will be affected. Always check cables to these components.

- Check wiring between:
^ Connector 24/2 terminal C5 and control module # B15.
^ Accelerometer terminal 1 and engine control module # B1.
^ A/C pressure sensor terminal 3 and engine control module # B29 for a short-circuit to ground.

^ Then proceed to Verification section below.





Checking Signal Cable
- Ignition off.
- Tank pressure sensor disconnected.
- Ignition on.
- Connect a voltmeter between tank pressure sensor connector terminal 3 (engine control module side) and ground.
- The voltmeter should read approx. 6 Volts.

If reading is OK:
^ Proceed to Checking Fuel Tank Pressure Sensor section below.

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

Checking Signal Cable Resistance To Ground
- Ignition off.
- Wait for approx. 150 seconds (cars with immobilizer 245 seconds).
- Tank pressure sensor disconnected.
- Connect an ohmmeter between fuel tank pressure sensor connector terminal 3 (engine control module side) and ground.
- Does the ohmmeter read infinite resistance?

Yes:
^ Proceed to test step below.

No:
^ Proceed to Checking Signal Cable Between Fuel Tank Pressure Sensor And Connector 24/4 section below.





Checking Connector 24/4
- Ignition off.
- Tank pressure sensor disconnected.
- Check connector 24/4 for contact resistance or oxidation and remedy.
- Assemble connector 24/4.
- Ignition on.
- Connect a voltmeter between tank pressure sensor connector terminal 3 (engine control module side) and ground.
- The voltmeter should read approx. 6 Volts.

If reading is OK:
^ The diagnostic trouble code has been caused by loose connections in connector 24/4.
^ Then proceed to Verification section below.

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





Checking Signal Cable Between Connector 24/4 And Fuel Tank Pressure Sensor
- Tank pressure sensor disconnected.
- Disassemble connector 24/4.
- Ignition on.
- Connect a voltmeter between connector 24/4 terminal E5 (engine control module side) and ground.
- The voltmeter should read approx. 6 Volts.

If reading is OK:
^ Check cable between fuel tank pressure sensor terminal 3 and connector 24/4 terminal E5 for an open-circuit.
^ Then proceed to Verification section below.

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





Checking Connector 24/2
- Ignition off.
- Tank pressure sensor disconnected.
- Connector 24/4 disassembled.
- Check connector 24/2 for contact resistance or oxidation and remedy.
- Assemble connector 24/2.
- Ignition on.
- Connect a voltmeter between connector 24/4 terminal E5 (engine control module side) and ground.
- The voltmeter should read approx. 6 Volts.

If reading is OK:
^ The diagnostic trouble code has been caused by loose connections in connector 24/2.
^ Then proceed to Verification section below.

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





Checking Signal Cable Between Connector 24/4 And 24/2
- Disassemble connector 24/2.
- Ignition on.
- Connect a voltmeter between connector 24/2 terminal C6 (engine control module side) and ground.
- The voltmeter should read approx. 6 Volts.

If reading is OK:
^ Check cable between connector 24/2 terminal C6 and connector 24/4 terminal E5 for an open-circuit.
^ Then proceed to Verification section below.

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





Checking The Engine Control Module Connector
- Ignition off.
- Wait for approx. 150 seconds (cars with immobilizer 245 seconds).
- Connector 24/2 disassembled.
- Check engine control module connector for contact resistance or oxidation and remedy.
- Connect engine control module.
- Ignition on.
- Connect a voltmeter between connector 24/2 terminal C6 (engine control module side) and ground.
- The voltmeter should read approx. 6 Volts.

If reading is OK:
^ The diagnostic trouble code was caused by loose connections in the engine control module connector.
^ Then proceed to Verification section below.

If reading is incorrect:
^ Check cable between connector 24/2 terminal C6 and engine control module # B31 for an open-circuit.
^ Then proceed to Verification section below.





Checking Signal Cable Between Fuel Tank Pressure Sensor And Connector 24/4
- Ignition off.
- Wait for approx. 150 seconds (cars with immobilizer 245 seconds).
- Disassemble connector 24/4.
- Connect an ohmmeter between connector 24/4 terminal E5 (engine control module side) and ground.
- The ohmmeter should read between 0.5 Meg Ohms and infinite resistance.

If reading is OK:
^ Check cable between fuel tank pressure sensor terminal 3 and connector 24/4 terminal E5 for a short-circuit to ground.
^ Then proceed to Verification section below.

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





Checking Signal Cable Between Connector 24/4 And 24/2
- Ignition off.
- Disassemble connector 24/2.
- Connect an ohmmeter between connector 24/2 terminal C6 (engine control module side) and ground.
- The ohmmeter should read between 0.5 Meg Ohms and infinite resistance.

If reading is OK:
^ Check cable between connector 24/4 terminal C6 and connector 24/2 terminal E5 for a short-circuit to ground.
^ Then proceed to Verification section below.

If reading is incorrect:
^ Check signal cable between connector 24/2 terminal C6 and engine control module # B31 for a short-circuit to ground.
^ Then proceed to Verification section below.





Checking Fuel Tank Pressure Sensor
- Ignition off.
- Connect fuel tank pressure sensor.
- Start the engine and idle it for a few minutes.
- Read diagnostic trouble code Status Message.

If Status Massage displays a Permanent Fault:
^ Try a new tank pressure sensor.
^ Then proceed to Verification section below.

If Status Message displays an Intermittent Fault:
^ The diagnostic trouble code has been caused by loose connections in the fuel tank pressure sensor connector. Check connector for contact resistance or oxidation and remedy.
^ Then proceed to Verification section below.





Verification
- After carrying out the repair, check that the fault has been remedied as follows.
- Ignition off.
- Ensure that fuel tank pressure sensor, A/C pressure sensor, accelerometer and engine control module are connected.
- Connectors 24/2 and 24/4 connected.
- Ignition on.
- Erase all diagnostic trouble codes.
- Start the engine and idle it.
- Does the diagnostic trouble code recur?

No:
^ Fault corrected

Yes:
^ 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.
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