Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Self-Diagnostic System: Notes
Volvo C70, S70 and V70 models use the Motronic 4.4 engine management system. System uses a single Electronic Control Module (ECM) to control fuel injection and ignition systems. This system is similar to the Motronic 4.4 system used on S90 and V90 vehicles.
Signals from various sensors are monitored continuously. If certain signals are lost or become faulty, ECM will adopt fixed substitute values (limp-home mode) to enable vehicle to be driven for certain failures. Substitute values can be adopted for Engine Coolant Temperature (ECT) sensor signal, Throttle Position (TP) sensor signal, Mass Airflow (MAF) sensor signal, and Heated Oxygen Sensor (HO2S) signal.
ECM stores Diagnostic Trouble Codes (DTCs) differently in accordance with a predetermined pattern. An emission related fault must be present for a predetermined number of intervals before ECM permanently stores a DTC and illuminates Malfunction Indicator Light (MIL). If fault is cleared before a specified interval has passed, DTC is erased from memory. There are 3 main types of intervals:
- Trip - All diagnostic functions have been performed.
- Running Cycle - Fuel trim (closed loop) has been initiated.
- Time - Time in seconds.
If a fault disappears for any reason after DTC has been recorded permanently by ECM, DTC information will be retained by ECM. Each time the fault occurs, first counter will advance one. Each trip completed without a reoccurrence, a second counter will count down from 3 to zero. When second counter has reached zero, MIL will extinguish (if illuminated) and a third counter will start counting down. The third counter counts number of warm-up cycles (starting at 40). A warm-up cycle is when engine temperature is less than 104°F (40°C) at engine start and exceeds 183°F (84°C). When third counter reaches zero, DTC is erased from ECM memory. If a fault reoccurs, the second and third counter revert to their original settings and the first counter advances one.
Faults are recorded in ECM memory in the form of Diagnostic Trouble Codes (DTCs). Codes can be displayed using Volvo Scan Tool (998-8686) or generic scan tester connected to OBD-II Data Link Connector (DLC). DLC is located in center console in front of gear shift lever. See Figure.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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