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Home >> Volvo >> 1998 >> S70 Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Diagnostic Tests >> DTC P0450/EFI 621, DTC P0451/EFI 621, DTC P0452/EFI 621 & DTC P0453/EFI 621 >> Diagnosis (Signal Sporadic)

Diagnosis (Signal Sporadic)

  1. Connect scan tool. See RETRIEVING & ERASING DTCs  under SELF-DIAGNOSTIC SYSTEM. If fault is PERMANENT, go to next step. If fault is INTERMITTENT check the following:
    • Fuel tank pressure sensor and ECM connectors for loose connections.
    • Intermittent short to ground in circuit between fuel tank pressure sensor terminal No. 3 and ECM terminal B15.
    • Intermittent open in circuit between fuel tank pressure sensor terminal No. 2 and ECM terminal B3.
    • Intermittent open in circuit between fuel tank pressure sensor terminal No. 1 and ECM terminal B28.
    • Fuel tank pressure sensor power supply is common to A/C pressure sensor, atmospheric pressure sensor and accelerometer power cables. If anything happens to any of the power supply, all four components will be affected.
    • Intermittent short to supply voltage in circuit between A/C pressure sensor terminal No. 3 and ECM terminal B29.
    • Intermittent short to supply voltage in circuit between atmospheric pressure sensor terminal No. 1 and ECM terminal B15.
    • Intermittent short to supply voltage in circuit between accelerometer terminal No. 1 and ECM terminal B1.
    Repair as necessary. After repairs, go to step  8.
  2. Turn ignition off. Check for contact resistance and oxidation at fuel tank pressure sensor harness connector, ECM harness connector, and bulkhead connectors 24/2 and 24/4. Repair as necessary. Ensure fuel tank pressure sensor and ECM are connected. Start engine and idle. Wait at least 5 minutes. With scan tool in DIAGNOSTIC MODE, read off DTC. If DTC P0450/EFI 621 is stored, DTC should have an INTERMITTENT status. If status is INTERMITTENT, go to step 8. If status is not INTERMITTENT, go to next step.
  3. Check for loose connections at fuel tank pressure sensor and/or ECM harness connector. Check for an intermittent open in circuit between fuel tank pressure sensor terminal No. 3 to ECM terminal B15. See Figure. Check for an intermittent open in circuit between fuel tank pressure sensor terminal No. 2 and ECM terminal B31. Check for an intermittent open in circuit between fuel tank pressure sensor terminal No. 1 and ECM terminal B28.
  4. Check for intermittent short to supply voltage in following circuits:
    • A/C Pressure Sensor Terminal No. 3 To ECM Terminal B29
    • Atmospheric Pressure Sensor Terminal No. 1 To ECM Terminal B15
    • Accelerometer Terminal No. 1 To ECM terminal B1
    Reinstall all components. Start engine and let idle for 5 minutes. Using scan tool, read DTCs. If DTC P0450/EFI 621 is stored in memory, it should have an INTERMITTENT status. If status is not INTERMITTENT, go to next step. If status is INTERMITTENT, go to step  8.
    5. NOTE: DTCs may be stored for A/C pressure sensor. Erase codes when fault-tracing is completed.
  5. Turn ignition off. Ensure fuel tank pressure sensor harness connector is connected. Disconnect A/C pressure sensor. A/C pressure sensor is located at right front of engine compartment. See Figure. Start engine and let idle for 5 minutes. Using scan tool, read DTC. If DTC P0450/EFI 621 is stored in memory, DTC should have an INTERMITTENT status. If status is INTERMITTENT, replace A/C pressure sensor. After repairs go to step  8. If status is not INTERMITTENT, go to next step.
    6. NOTE: DTCs may be stored for A/C pressure sensor. Erase codes when fault-tracing is completed.
  6. Turn ignition off. Ensure fuel tank pressure sensor harness connector is connected. Ensure A/C pressure sensor is connected. Disconnect accelerometer. Accelerometer is located at front of engine compartment. See Figure. Start engine and let idle for 5 minutes. Using scan tool, read DTCs. If DTC P0450/EFI 621 is stored in memory, DTC should have an INTERMITTENT status. If status is INTERMITTENT, replace accelerometer. After repairs, go to step  8. If status is not INTERMITTENT, go to next step.
    7. NOTE: DTCs may be stored for A/C pressure sensor. Erase codes when fault-tracing is completed.
  7. Turn ignition off. Ensure fuel tank pressure sensor harness connector is connected. Ensure accelerometer harness connector is connected. Disconnect atmospheric pressure sensor harness connector. Start engine and let idle for 5 minutes. Using scan tool, read DTCs. If DTC P0450/EFI 621 is stored in memory, it should have an INTERMITTENT status. If status is INTERMITTENT, replace atmospheric pressure sensor. See Figure. After repairs, go to next step. If status is not INTERMITTENT, replace fuel tank pressure sensor. See Figure. After repairs, go to next step.
  8. Turn ignition off. Reconnect all connectors and components. Disconnect scan tool from VADIS station and use it in stand-alone mode. Test drive vehicle. Using scan tool, read DTCs. If DTC P0450/EFI 621 is stored in memory, DTC should have an INTERMITTENT status. If status is INTERMITTENT, fault was corrected. If status is not INTERMITTENT, fault was not found. Repeat test, starting in step  1.
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