Self-Diagnostic System: Notes

WARNING: This page is about a different car, the 1996 Volvo 850. However, it is still accessible from the selected car via links, so may be relevant.

850 Turbo, A/T equipped models use the Motronic 4.3 control system. All 850 models with manual transmission, and 850 models with automatic transmission sold in California, Massachusetts, New Jersey, New York, and possibly other states, use the Motronic 4.4 control system. See TESTS W/ CODES article.

Motronic 4.3 system uses a single Electronic Control Module (ECM) to control fuel injection and ignition systems. 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.

NOTE: To avoid confusion if there is an intermittent malfunction with Malfunction Indicator Light (MIL), carefully read following text.

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). DTCs can be displayed using Volvo Scan Tool (998-8686 ) or generic scan tool connected to Data Link Connector (DLC). DLC is located in center console in front of gear shift lever. See Figure.