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Engine Controls - Tests W/codes - Non-Turbo: Diagnosis Volvo 850 I

Testing & Diagnostics ~710 words

DIAGNOSTIC UNIT "A" LED DOES NOT FLASH

  1. Disconnect diagnostic unit "A". Turn ignition on. Check for voltage at diagnostic connector terminal No. 4. If voltage is not present, check fuse and wiring. If voltage is present, turn ignition off.
  2. Connect an ohmmeter between diagnostic connector socket No. 8 and ground. Ohmmeter should indicate approximately zero ohms. If reading is not approximately zero ohms, check wiring. If wiring is okay, replace diagnostic unit "A".

DIAGNOSTIC UNIT "A" LED FLASHES BUT ECU DOES NOT RESPOND

  1. Turn ignition on. Check for voltage at diagnostic socket No. 2 (fuel injection system) or No. 6 (ignition system). Approximately 10 volts should be present. If approximately 10 volts is not present, check wiring.
  2. Turn ignition off. Connect Measuring Unit (9813190). See «MEASURING UNIT»(ref-12934-S34075947862000122900000) . Connect an ohmmeter between socket No. 2 (fuel injection system) or No. 6 (ignition system) and measuring unit terminal No. 35. If continuity is present, repeat test using a known good ECU.

FUEL INJECTION SYSTEM DIAGNOSTICS

Fuel injection ECU carries out continuous checks. The following sensors and components supply fuel injection system ECU with information.

  1. Mass Airflow Sensor (MAF Sensor)
  2. Throttle Switch
  3. Engine Temperature Sensor
  4. Heated Oxygen Sensor (HO2S)
  5. A/C Compressor
  6. Speedometer
  7. Automatic Transmission ECU
  8. Ignition ECU, With Signals Indicating: Engine Speed And Cooling Fan

IGNITION SYSTEM DIAGNOSTICS

Ignition system ECU carries out continuous checks. The following sensors and components supply ignition system ECU with information.

  1. Injectors
  2. Idle Air Control (IAC) Valve
  3. Fuel Pump
  4. Main Fuel System Relay
  5. HO2S Heating
  6. Emission Warning Light

ENTERING SELF-DIAGNOSTICS - FUEL INJECTION SYSTEM

Note. To perform diagnosis, turn ignition on. Function selector cable must be in diagnostic unit "A", socket No. 2. (Схема №1)

Diagnostic Test Mode No. 1 (On-Board Diagnosis)

Press test button one time quickly on diagnostic unit "A" to display codes. (Схема №1) ECU can store 3 faults at a time in diagnostic test mode No. 1. Diagnostic trouble codes are stored when a faulty signal is detected.

Diagnostic Test Mode No. 2 (Function Testing)

Press test button 2 times to activate test mode No. 2. LED should flash rapidly. ECU should deliver an acknowledgment code when a signal is received from the following

  1. 3-3-2 - Throttle switch (when throttle leaves idling position).
  2. 3-3-3 - Throttle switch (when throttle leaves full-load position).
  3. 1-1-4 - Ignition system ECU (when cooling fan is running).
  4. 1-3-4 - Low-pressure switch (when A/C compressor starts).
  5. 1-2-4 - AW50-42 A/T ECU (when gear selector lever is moved to or from a drive position.
  6. 3-3-1 - Ignition system ECU (when transmitting speed signals).

Diagnostic Test Mode No. 3 (Control Testing)

Press test button 3 times to activate test mode No. 3. ECU responds by activating components in following order

  1. Injectors at 12 Hz for 10 seconds (5-second pause).
  2. IAC valve at one Hz for 10 seconds (5-second pause). This sequence is repeated 3 times.

ENTERING SELF-DIAGNOSTICS - IGNITION SYSTEM

Note. To perform diagnosis, turn ignition on. Function selector cable must be in diagnostic unit "A", socket No. 6. (Схема №1)

Press test button one time quickly on diagnostic unit "A" to display codes. (Схема №1) ECU can record and store 13 faults at a time in diagnostic test mode No. 1. Diagnostic trouble codes are stored when a faulty signal is detected.

Press test button 2 times to activate test mode No. 2. LED should flash rapidly. ECU should deliver an acknowledgment code when a signal is received from the following

  1. 1-4-1 - VSS (as flywheel rotates).
  2. 3-4-2 - CMP (as camshaft rotates).
  3. 3-4-3 - Speedometer (as front wheels rotate).
  4. 3-4-4 - Fuel injection ECU (when throttle switch is operated by opening throttle).

Press test button 3 times to activate test mode No. 3. ECU responds by activating components in following order

  1. Cooling fan at half speed for 15 seconds.
  2. Cooling fan at full speed for 15 seconds (15-second pause).
  3. Variable-flow intake manifold solenoid valve for 2 Hz for 5 seconds (5-second pause).
  4. Speedometer for 5 seconds by generating a speed signal for approximately 1500 RPM (5-second pause).

The sequence is repeated 3 times.

FUEL INJECTION DIAGNOSIS

This section will cover codes dealing with fuel injection ECU testing. Codes are followed by an explanation of how to test and repair affected circuit.

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