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Home >> Volvo >> 1998 >> S70 GLT >> 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 Too High)

Diagnosis (Signal Too High)

  1. Connect scan tool. See RETRIEVING & ERASING DTCs  under SELF-DIAGNOSTIC SYSTEM. If signal is PERMANENT, go to next step. If signal is INTERMITTENT, check the following:
    • Loose connection at fuel tank pressure sensor.
    • Loose connection at ECM harness connectors.
    • Loose connection at bulkhead connectors 24/2 and 24/4.
    • Intermittent short in supply voltage in circuit between tank pressure sensor terminal No. 2 and ECM B31 via bulkhead connector 24/4 terminal No. E5.
    • Intermittent short in supply voltage in bulkhead connector 24/2 terminal C6 circuit.
    • Intermittent open in circuit between tank pressure sensor terminal No. 1 and ECM terminal B28 via bulkhead connector 24/4 terminal E6.
    • Intermittent open in bulkhead connector 24/2 terminal C7 circuit.
    Repair as necessary. After repairs, go to step  7.
  2. Turn ignition off. Wait approximately 2 minutes. Disconnect fuel tank pressure sensor. See Figure. Using DVOM, measure resistance between ground and fuel tank pressure sensor harness connector terminal No. 1. If resistance reads approximately zero ohms, go to step  4. If resistance does not read approximately zero ohms, go to next step.
  3. Turn ignition off. Check for contact resistance and oxidation at bulkhead connector 24/4. See Figure. Ensure ECM is securely connected. Ensure bulkhead connector 24/4 is connected. Using DVOM , measure resistance at fuel tank pressure sensor harness connector terminal No. 1. Resistance should be approximately zero ohms. If resistance is within specification, go to step  7. If resistance is not within specification, check for an open in circuit between fuel tank pressure sensor terminal No. 2 and ECM terminal B28. See Figure. Repair as necessary. After repairs, go to step  7.
  4. Turn ignition on. Disconnect fuel tank pressure sensor harness connector. Using DVOM, measure voltage between ground and fuel tank pressure sensor harness connector terminal No. 2. Voltage should be 5-6 volts. If voltage is as specified, go to step  6. If voltage is less than specified, go to next step. If voltage is more than specified, check for short to voltage in circuit between fuel tank pressure sensor terminal No. 2 and ECM terminal B31. Repair as necessary. See Figure. After repairs, go to step  7.
  5. Turn ignition off. Disconnect fuel tank pressure sensor harness connector. Check for contact resistance and oxidation at ECM harness connector, and bulkhead connectors 24/2 and 24/4. See Figure. Repair as necessary. Ensure ECM is securely connected. Connect bulkhead connectors 24/2 and 24/4. Turn ignition on. Using DVOM, measure voltage between ground and fuel tank pressure sensor connector terminal No. 2. Voltage should be approximately 5 volts. If voltage is as specified, go to step  7. If voltage is not as specified, check for an open in signal circuit between fuel tank pressure sensor terminal No. 3 and ECM terminal B31. Repair as necessary. After repairs, go to step  7.
  6. Turn ignition off. Ensure fuel tank pressure sensor is connected. Start and idle engine for at least one minute. With scan tool in DIAGNOSTIC MODE, check DTC status message. If an INTERMITTENT fault is not displayed, replace fuel tank pressure sensor. After repairs, go to next step. If INTERMITTENT fault is displayed, DTC was caused by loose connection in fuel tank pressure sensor. Check for contact resistance and oxidation at fuel tank pressure sensor harness connector. Repair as necessary. After repairs, go to next step.
  7. Turn ignition off. reconnect all components. Start engine and idle. With scan tool in DIAGNOSTIC MODE, check DTC status message. If DTC is stored, DTC should have INTERMITTENT status. If DTC is INTERMITTENT, fault has been corrected. If DTC is not INTERMITTENT, repeat testing, starting with step  1.
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