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Engine Controls - Tests W/codes Volvo 960 I

Testing & Diagnostics 5 illustrations ~3629 words

INTRODUCTION

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed with SELF-DIAGNOSTIC SYSTEM. If no fault codes or only pass codes are present, proceed to TESTS W/O CODES article in the ENGINE PERFORMANCE Section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.).

Note. All voltage tests should be performed using a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless specifically stated otherwise in testing procedures.

SELF-DIAGNOSTIC SYSTEM

960 uses a Motronic 1.8 diagnostic system, which uses a single Electronic Control Unit (ECU) to control fuel injection and ignition systems. In addition, Motronic 1.8 diagnostic system determines whether A/C compressor may be switched on, reduces engine torque in response to a signal from automatic transmission and controls radiator fan.

Diagnostic unit for retrieving codes is located in engine compartment, in front of left strut assembly. Diagnostic unit is equipped with an LED indicator, activation button and function select cable. (Scheme 18)

Diagnostic unit output socket No. 2 is used to retrieve all codes. Once selector cable has been inserted in correct slot, depressing button once, twice or 3 times selects from one of 3 control (fault tracing) functions. Faults stored in ECU memory are read by observing LED flashes. Diagnostic system stores 18 fault codes.

All fault codes contain 3 digits (example: 4-1-3). Since codes have 3 digits, each code requires 3 series of flashes. A 3-second interval separates series of flashes. (Scheme 19)

Scheme 18

Scheme 18: SELF-DIAGNOSTIC SYSTEM
Scheme 18: SELF-DIAGNOSTIC SYSTEM

Scheme 19

Scheme 19
Scheme 19

RETRIEVING CODES

CAUTIONNever disconnect or connect ECU connector with ignition switch in ON position. Ensure ignition is off and fuse No. 24 is removed.

ECU is equipped with diagnostic functions in form of self-diagnostics (Test Mode No. 1), function testing (Test Mode No. 2) and control testing (Test Mode No. 3). Access to diagnostic system is provided by socket No. 2 on diagnostic unit with ignition on.

Test Mode No. 1 (Retrieving Codes)

  1. ECU can record 18 fault codes. Fault codes stored in memory can be displayed by pressing test button "A" on diagnostic unit for an instant. Control unit memory can retain codes from 10 minutes to 24 hours after interruption of electrical supply.
  2. Control unit will begin to use a faulty or missing signal immediately after it has been corrected rather than remaining in limp-home mode. Fault code, however, will remain in memory.
  3. To retrieve codes, open diagnostic unit cover and connect test lead to socket No. 2. Turn ignition on. Enter test mode No. 1 by pressing test button once for 1-3 seconds.
  4. Observe LED, and count number of flashes in 3 digit series comprising a fault code. Because series are displayed at 3-second intervals, codes can be easily distinguished.
  5. If a fault code is retrieved, refer to «FAULT CODES»(/volvo/960/i-1990-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes) table under FAULT CODE DEFINITION. Depress push button again, and check for additional codes. Depress push button a third time if necessary. If first code repeats, no other codes are present. Control unit can store all 18 codes simultaneously.

Test Mode No. 2

This function is activated by briefly pressing test button "A" 2 times, causing LED to rapidly flash. Control unit will flash a code indicating receipt of a signal from following components

  1. 3-3-2 - Throttle switch (throttle moved from idle).
  2. 3-3-3 - Throttle switch (throttle moved from WOT).
  3. 1-2-4 - Starter inhibitor switch, when gear selector is moved from a drive position to N or P.
  4. 1-4-1 - Timing pick-up, when starter motor is running.
  5. 1-1-4 - ECC control panel, when A/C button is depressed or released.
  6. 1-3-4 - Relay in ECC power unit energizing A/C compressor clutch when A/C is on.

Test Mode No. 3

This function is activated by briefly pressing test button "A" 3 times. Control unit will respond by activating following components in order

  1. Radiator fan at half speed for 3 seconds.
  2. Radiator fan at full speed for 3 seconds.
  3. Fuel injectors.
  4. Idling (CIS) valve.
  5. Relay in ECC power unit, resulting in A/C clutch operation.

CLEARING CODES

  1. Turn ignition on. Display fault codes. Operate test button for more than 5 seconds. Release test button. LED should light after 3 seconds. Press button again for more than 5 seconds. Release button. LED should be out.
  2. Ensure fault codes have been cleared by pressing test button once for more than one second (but not more than 3 seconds). Fault codes have been cleared if code 1-1-1 is displayed.

FAULT CODE DEFINITION

CodeFaultRepair
1-1-1No FaultsNone
1-1-2ECUReplace ECU
1-1-3Fuel InjectorsCheck Fuel Injectors
1-2-1Mass Airflow Signal(1) Check Airflow Meter & Main Relay
1-2-3Coolant Temperature Sensor Signal(1) Check Sensor
1-3-1Timing Pick-Up Signal(2)
1-3-2Battery Voltage(2)
1-4-3No Front Knock Sensor Signal(2)
2-1-2Oxygen Sensor Signal(1) Check Oxygen Sensor
2-1-4Timing Pick-Up Signal(2)
2-2-3No Idle Valve Signal(2)
2-3-1Lambda Rich/Lean In Part Load Range(2)
2-3-2Lambda Rich/Lean At Idle(2)
2-3-3Idle Control Not In Range(2)
2-4-1EGR Flow Too Low(2)
2-4-3Throttle Switch Signal Absent Or Faulty(2)
3-1-1Speedometer Signal(2)
3-1-4Camshaft Sensor Signal(2)
3-2-2Airflow Meter Hot Wire(2)
4-1-3EGR Temperature Sensor Absent/Faulty(2)
4-3-3No Rear Knock Sensor Signal(2)
5-1-2Short Term Fuel Trim(2)
(1) See SYSTEM/COMPONENT TESTS article in the ENGINE PERFORMANCE Section. (2) See FAULT CODE TESTING under SELF-DIAGNOSTIC SYSTEM.
(1)See SYSTEM/COMPONENT TESTS article in the ENGINE PERFORMANCE Section.
(2)See FAULT CODE TESTING under SELF-DIAGNOSTIC SYSTEM.

FAULT CODES

ECU LOCATION

ECU is located above accelerator pedal.

Identifying Engine Compartment Motronic 1.8 Engine Management Locations. Scheme 20

Scheme 20: Identifying Engine Compartment Motronic 1.8 Engine Management Locations
Scheme 20: Identifying Engine Compartment Motronic 1.8 Engine Management Locations

CONNECTING MEASURING UNIT TO ECU

Note. Measuring unit may also be known breakout box.

CAUTIONWhile connecting and disconnecting adapter, ECU must not have live voltage as it could be damaged.

Connect measuring unit. Turn ignition off. Remove fuse No. 1 (11B/1) in central relay unit. Disconnect ECM. Connect measuring unit to ECU connector. (Scheme 21)

Scheme 21

Scheme 21
Scheme 21

CODE 1-3-1 OR 2-1-4 (TIMING PICK-UP SIGNAL)

  1. Enter test mode No. 2. See TEST MODE NO. 2 under «RETRIEVING CODES»(/volvo/960/i-1990-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes__retrieving-codes) . Operate starter motor. Code 1-4-1, indicating a timing pick-up signal, should be displayed.
  2. Disconnect ECU connector. Connect a voltmeter capable of measuring millivolts between ECU connector terminals No. 47 (Pink wire) and 48 (White/Black wire). Operate starter motor. Voltmeter should indicate 300-400 millivolts.
  3. Turn ignition off. Connect an ohmmeter between timing pick-up connector terminals No. 47 (Pink wire) and 48 (White/Black wire). Resistance should be approximately 200-400 ohms.
  4. Reconnect ECU with Measuring Unit (999-3070 ) connected to ECU. See «CONNECTING MEASURING UNIT TO ECU»(/volvo/960/i-1990-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes__connecting-measuring-unit-to-ecu) . Connect an ohmmeter between terminals No. 48 and 19. Resistance should be zero ohms. Measure resistance between terminals No. 48 and 30. Resistance should be zero ohms. On automatic transmission equipped vehicles, check test mode No. 1 if speed signal fault code is displayed. See TEST MODE NO. 1 under «RETRIEVING CODES»(/volvo/960/i-1990-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes__retrieving-codes) .

CODE 1-3-2 (BATTERY VOLTAGE)

  1. This code is set if battery voltage decreases to less than 8 volts or exceeds 16 volts for 5 seconds after engine start. To check, connect Measuring Unit (999-3070 ) to ECU. See «CONNECTING MEASURING UNIT TO ECU»(/volvo/960/i-1990-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes__connecting-measuring-unit-to-ecu) . Connect voltmeter between terminals No. 18 and 19.
  2. Start engine and check battery voltage. Check battery and charging system if voltage is too low or high.

CODE 1-4-3 OR 4-3-3 (NO FRONT/REAR KNOCK SENSOR SIGNAL)

Disconnect knock sensor connector and jumper terminals. Measure resistance between knock sensor terminal No. 2 (Green/Gray wire) and terminal No. 11 (Green wire) or terminal No. 29 (Brown/Orange wire), depending upon whether front or rear knock sensor is being checked. If zero ohms is present, replace knock sensor. Tighten sensor to 15 ft. lbs. (20 N.m).

CODE 2-2-3 (NO IDLE VALVE SIGNAL)

  1. Check operation of idle valve in test mode No. 3. See TEST MODE NO. 3 under «RETRIEVING CODES»(/volvo/960/i-1990-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes__retrieving-codes) . If valve does not operate, check wiring.
  2. Connect Measuring Unit (999-3070 ) to ECU. See «CONNECTING MEASURING UNIT TO ECU»(/volvo/960/i-1990-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes__connecting-measuring-unit-to-ecu) . Start engine. Connect voltmeter between terminals No. 4 and 24. Approximately 11 volts should be present. Connect voltmeter between terminals No. 22 and 24. Approximately 7.5 volts should be present.
  3. Turn engine off (ignition on). Using a voltmeter, check voltage at terminals No. 4 and 22. Voltage should be approximately 8-9 volts. If no voltage is present, check wiring to idle valve.
  4. Turn ignition off. Using an ohmmeter, check resistance across terminals No. 4 and 22. Resistance should be approximately 25 ohms. If not, replace idle valve.

CODE 2-3-1 (LAMBDA CONTROL RICH OR LEAN IN PART LOAD RANGE); OR CODE 2-3-2 (LAMBDA CONTROL RICH OR LEAN AT IDLE)

  1. Control unit receives information from oxygen sensor on whether fuel/air mixture is too rich or too lean in part-load and idling ranges. Control unit adap-tive system compensates for this by making mixture leaner or richer as necessary. If mixture must be compensated excessively, a fault code is set.
  2. Start engine. Connect voltmeter between terminals No. 1 and 2 in starter motor 2-pin connector. Voltmeter should indicate battery voltage. If no voltage is present, check fuse No. 30.
  3. Stop engine. Disconnect starter motor connector. Connect ohmmeter between starter motor connector terminals No. 1 and 2. Ohmmeter should show 3-13 ohms, depending on resistor temperature.
  4. Connect Measuring Unit (999-3070 ) to ECU. See «CONNECTING MEASURING UNIT TO ECU»(/volvo/960/i-1990-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes__connecting-measuring-unit-to-ecu) . Start engine. Connect voltmeter between terminals No. 28 and 30. After a short interval, voltmeter should oscillate between 0.1-1.0 volt.
  5. If voltage remains constant a zero volts, sensor is interpreting fuel/air mixture as lean. If voltage is constant at one volt, sensor is interpreting fuel/air mixture as rich.
  6. If either fault code 2-3-1 or 2-3-2 is displayed and voltmeter is oscillating between 0.1-1.0 volt, Lambda control is correctly adjusting CO content even though ECU is indicating fault.

CODE 2-3-3 (IDLE CONTROL NOT IN RANGE)

  1. If control unit has to open or close idling valve too much to maintain constant idling conditions, control unit will interpret this as a fault and record a fault code.
  2. Start engine, and run it until it reaches normal operating temperature. Ensure gear selector is in NEUTRAL position and A/C is off. To determine whether an air leak is present, clamp air valve hose and observe engine speed. If engine speed exceeds 600-700 RPM, air leakage is present or throttle disc is incorrectly adjusted.

CODE 2-4-1 (EGR FLOW TOO LOW)

  1. Enter test mode No. 3. See TEST MODE NO. 3 under «RETRIEVING CODES»(/volvo/960/i-1990-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes__retrieving-codes). Turn ignition on. Press test button on diagnostic unit 3 times for more than one second each. Light should flash as EGR converter is activated. Turn ignition off.
  2. If EGR converter is not activated, measure resistance between pins No. 6 (Blue wire) and 15 (Red/Green wire). Resistance should be about 75-95 ohms. If resistance is not as specified, check wiring and connectors.
  3. Disconnect EGR converter connector, located next to power steering fluid reservoir. (Scheme 22) Remove wire directly opposite Black/White wire between pin No. 1 and control unit. Reconnect connector.
  4. Start engine, and run it until it reaches normal operating temperature. Touch loose lead to engine ground. If engine starts to run unevenly, EGR system is operating correctly.

Scheme 22

Scheme 22
Scheme 22

CODE 2-4-3 (THROTTLE SWITCH SIGNAL ABSENT OR FAULTY)

  1. Enter test mode No. 2. See TEST MODE NO. 2 under «RETRIEVING CODES»(/volvo/960/i-1990-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes__retrieving-codes) . Turn throttle slightly. Throttle function is correct in idling position if flashing code 3-3-2 is displayed.
  2. Turn throttle to full-load position and release. Throttle function is correct in full-load position if flashing code 3-3-3 is displayed.
  3. Connect Measuring Unit (999-3070 ) to ECU. See «CONNECTING MEASURING UNIT TO ECU»(/volvo/960/i-1990-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes__connecting-measuring-unit-to-ecu) . Turn ignition on. Connect voltmeter between terminals No. 30 and 53. Voltmeter should indicate about 0.5 volts at idle and about 4.5 volts at full load.
  4. Connect voltmeter between terminals No. 12 and 30. Voltmeter should indicate 5 volts. Turn ignition off. Ensure terminal No. 30 is grounded. Connect an ohmmeter between terminals No. 19 and 30. Ohmmeter should indicate zero ohms.

CODE 3-1-1 (SPEEDOMETER SIGNAL)

  1. Control unit is dependent on this signal for WOT enrichment, fan control, etc. A fault code will be set if speed exceeds 3390 RPM, load signal corresponds to part load and signal is absent for 3 seconds.
  2. To check speedometer signal, raise vehicle with rear wheels suspended. Connect Measuring Unit (999-3070 ) to ECU. See «CONNECTING MEASURING UNIT TO ECU»(/volvo/960/i-1990-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes__connecting-measuring-unit-to-ecu) . Connect voltmeter between terminals No. 9 and 19. Turn ignition on. Spin rear wheels, and check voltmeter. Voltage should be 0.1-12.0 volts.
  3. If voltage is not present, check wiring between control unit and instrument cluster. Connect ohmmeter between terminal No. 9 and terminal at rear of instrument cluster (Green/Orange wire). Ohmmeter should indicate zero ohms.
  4. If no reading is obtained, check wiring between instrument cluster and control unit. If reading is obtained, check wiring between instrument cluster and rear axle. On A/T models, check test mode No. 1 if speed signal fault is obtained. See TEST MODE NO. 1 under «RETRIEVING CODES»(/volvo/960/i-1990-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes__retrieving-codes) .

CODE 3-1-4 (CAMSHAFT SENSOR SIGNAL)

  1. Camshaft sensor enables control unit to determine which cylinder requires fuel and ignition. A fault code is recorded if signal remains constantly high or low for more than 30 seconds.
  2. To check camshaft sensor signal, remove fuse No. 31 to prevent engine from starting and connect Measuring Unit (999-3070 ) to ECU. See «CONNECTING MEASURING UNIT TO ECU»(/volvo/960/i-1990-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes__connecting-measuring-unit-to-ecu) . Turn ignition switch to ON position. Connect voltmeter across terminals No. 8 and 19. Operate starter motor. Voltage should oscillate between .1 and .5 volt. Install fuse No. 31.
  3. If signal is absent or faulty, ensure voltage across terminals No. 10 and 30 is about 11 volts. Turn ignition off. Ensure terminal No. 30 is grounded. Connect an ohmmeter between terminals No. 30 and 19. Ohmmeter should indicate zero ohms.

CODE 3-2-2 (AIRFLOW METER HOT WIRE)

  1. Approximately 4 volts is routed to platinum wire in airflow meter from ECU terminal No. 5. Ground is supplied from ECU terminal No. 7. Fault code is set if voltage between ground and terminal No. 7 does not exceed 2.5 volts.
  2. Turn ignition off. Connect Measuring Unit (999-3070 ) to ECU. See «CONNECTING MEASURING UNIT TO ECU»(/volvo/960/i-1990-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes__connecting-measuring-unit-to-ecu) . To ensure airflow meter is grounded, connect ohmmeter between terminals No. 19 and 26. Zero ohms should be present. Connect ohmmeter between airflow meter connector terminal No. 1 (Brown wire) and ground. Reading should be about zero ohms.
  3. Connect ohmmeter between terminals No. 7 and 26. Reading should be about 2.5-4.0 ohms. If resistance is not to specification, measure resistance between airflow meter terminals No. 2 (Brown/White wire) and 3 (Green/Yellow wire).
  4. Turn ignition on. Connect voltmeter between terminals No. 7 and 19. About 1.4 volts should be present. Start engine. Voltage should increase to 2.3-2.6 volts when idling. Voltage should be 2.3 volts with engine hot.
  5. If voltage reading is too low, connect voltmeter between terminals No. 25 and 19. Increase speed to 1800 RPM, and stop engine. Voltage should be about 4 volts. On A/T models, check test mode No. 1 if load signal fault code is displayed. See TEST MODE NO. 1 under «RETRIEVING CODES»(/volvo/960/i-1990-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes__retrieving-codes) .

CODE 4-1-3 (EGR TEMPERATURE SENSOR ABSENT/FAULTY)

Measure resistance between terminals No. 14 (Black wire) and 22 (Yellow/Black wire). Resistance should be 500-1000 ohms. If resistance is not 500-1000 ohms, check wiring, connectors and ground terminal on intake manifold.

Fault Condition

The ECM receives information from the HO2S on air/fuel mixture. If air/fuel mixture deviates from l=1, the short-term fuel trim compensates for it by adjusting the injection period. If the short-term fuel trim remains lean for more than 3 minutes and engine temperature exceeds 75°C (167°F), DTC 5-1-2 is set.

Substitute Value

None is provided.

Possible Sources

Faulty sensor signal or high fuel pressure.

Diagnostic Procedure

  1. Check MAF sensor signal. Start and warm up engine. Gear selector: neutral, A/C: off, engine warm. Power consumers such as engine coolant fan, heated rear window, etc. should be off. Using scan tool, select Volvo ST symbol to read off load signal. Value should read 2.3-2.4 volts at idle. If okay, go to next step. If not okay, go to step 16 .
  2. Check vacuum hose to pressure regulator. Remove vacuum hose from pressure regulator. Check hose to be sure that it is not blocked by blowing it through. Is hose OK? If yes, go to next step if engine equipped with quick-release coupling. If engine is not equipped with quick-release coupling, go to 4 . If no, check hose and nipple and fix fault.
  3. Connect pressure gauge. Turn ignition off. Fit Pressure Gauge (999 5011) with Nipple (998 9725) and Adapter (999 5479) before use. If draining unit absent, instead of Fitting Nipple (998 9725), fit Hose (999 5116) and Plug (999 5266). Connect Draining Unit (981 2270), (981 2273) and (981 2282) to Nipple (998 9725) on pressure gauge. Set valve on Pressure Gauge (999 5011) to position 3 (valve should point towards Adapter (999 5479). Remove protective cap on valve which is located on fuel manifold. Connect adapter to valve in locked position. Go to step 5 .
  4. Connect pressure gauge. Turn ignition off. Connect Pressure Gauge (999 5011) between fuel lead and manifold. Use Hose (999 5116) and Nipple (999 5431). Plug free end of gauge with Plug (999 5266). Set valve on (999 5011) to position 1 (valve should point towards Hose (999 5116). Go to next step.
  5. Start fuel pump. Turn ignition off. Remove fuse No 23 in fuse box on left side of instrument panel. Remove FP relay in fuse box on left side of instrument panel position 2. Connect a lead between contacts 1 and 2 on relay base. Turn ignition on. Go to next step.
  6. Read off system pressure on pressure gauge. System pressure should read 300 kPa (3.0 kp/cm2) (43.5 psi). If pressure is okay, go to next step. If pressure is low, go to step 14 . If pressure is high, go to step 15 .
  7. Check fuel filter. Clamp together return lead and check if pressure rises. Pressure must not exceed 600 kPa (6.0 kp/cm2) (87.0 psi). Does pressure rise rapidly? If yes, go to next step. If no, install a new fuel filter.
  8. Check pressure regulator, loss of pressure. Connect vacuum pump to pressure regulator. Pump out air from regulator. Check that system pressure at same rate as regulator pressure. 300 kPa - negative pressure = system pressure. Disconnect hose from vacuum pump. System pressure should return to 300 kPa (43.5 psi). If okay, go to next step. If not okay, install new pressure regulator.
  9. Check pressure regulator, increase in pressure. Connect vacuum pump and Manometer (999 5230) to pressure regulator. Check that system pressure rises as same rate as regulator pressure. 300 kPa - negative pressure = system pressure. Disconnect hose from pressure tester. System pressure should return to 300 kPa (43.5 psi). If okay, go to next step. If not okay, install new pressure regulator.
  10. Check residual pressure. Switch off ignition. Remove lead between contacts 1 and 2 on relay base. Replace FP relay. Value should not fall below 200 kPa (29 psi) in less than 20 minutes. If okay, go to next step if engine equipped with quick-release coupling. If engine is not equipped with quick-release coupling, go to step 12 . If not okay, incorrect residual pressure can be due to leaks in injection valves, connectors, FP non-return valve, or hose. Fix as necessary.
  11. Disconnect pressure gauge. Turn ignition off. Start draining unit. Lock adapter (valve closed). Set valve on pressure gauge to mid position. If draining unit is absent, place paper under quick-release coupling to soak up any fuel spillage when pressure gauge is removed. Remove adapter from valve. Stop draining unit. Refit components. Do not forget to refit safety cap to valve. Go to step 13 .
  12. Disconnect pressure gauge. Turn ignition off. Place paper under fuel lead to soak up any fuel spillage when pressure gauge is removed. Remove pressure gauge. Any plastic tape on fuel pipes which is removed must be replaced. Go to next step.
  13. Connect breakout box to ECU. See «CONNECTING MEASURING UNIT TO ECU»(/volvo/960/i-1990-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes__connecting-measuring-unit-to-ecu) . Check all signals to ECU. See «PIN VOLTAGE CHARTS»(/volvo/960/i-1990-1994/remont/pin-voltage-charts/#engine-controls-pin-voltage-charts) article. Repair as necessary. Testing is completed.
  14. System pressure too low. Clamp together return lead and check if pressure rises. Pressure must not exceed 600 kPa (6.0 kp/cm2) (87.0 psi). Does pressure rise? If yes, pump and hose is fault-free. Try with a new pressure regulator. Measure system pressure again. Repair is completed. If no, check fuel pump filter. If filter is okay, try with a new fuel pump. Measure system pressure. Testing is completed.
  15. System pressure too high. Remove lead between contacts 1 and 2 on relay base. Remove return hose from pressure regulator. Blow through hose. Is hose okay? If yes, Try with a new pressure regulator. Measure system pressure. Testing is complete. If no, check if return hose is damaged or blocked. Clean and change. Measure system pressure. Testing is complete.
  16. Check MAF sensor ground lead. Turn ignition off. Disconnect MAF sensor. Connect an ohmmeter between MAF sensor connector contact No. 1 and ground. Ohmmeter should read approx. 0 ohms. If okay, check MAF sensor connector for contact resistance and oxidation. Repair as needed. Go to next step. If not okay, go to step 18 .
  17. Check load signal. Start and warm up engine. Gear selector: neutral, A/C: off, engine warm. Ensure engine coolant fan, heated rear window, etc. are off. Using scan tool, select Volvo ST symbol to read off load signal. Value should read 2.3-2.4 V at idle. If okay, testing is complete. If not okay, install new MAF and retest. Testing is complete.
  18. Check connector. Disconnect MAF sensor connector. Check 53-pin connector in left wheel-arch (C131) connector 15 for contact resistance and oxidation. Repair as needed. Ensure ECU is connected. Connect an ohmmeter between MAF sensor connector contact No. 1 and ground. Ohmmeter should read approx. 0 ohms. If okay, source of DTC is bad contact in connector. If not okay, check lead between MAF sensor connector contact No. 1 and control point on engine (31/33) for open. Go to next step.
  19. Check load signal. Start and warm up engine. Gear selector: neutral, A/C: off, engine warm. Ensure engine coolant fan, heated rear window, etc. are off. Using scan tool, select Volvo ST symbol to read off load signal. Value should read 2.3-2.4 V at idle. If okay, testing is complete. If not okay, install new MAF and retest. Testing is complete.

SUMMARY

If no hard fault codes (or only pass codes) are present, driveability symptoms exist or intermittent codes exist, proceed to the TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.

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