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

SELF-DIAGNOSTIC SYSTEM

850 turbo uses a Motronic 4.3 control system, which has a single Electronic Control Module (ECM) to control fuel injection and ignition systems. In addition, Motronic 4.3 control system incorporates an on-board diagnostic function. 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 oxygen sensor (HO2S) signal. (Scheme 1)

Note. To avoid confusion thinking 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

1. Trip - All diagnostic functions have been performed.
2. Running Cycle - Fuel trim (closed loop) has been initiated.
3. 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 one of 4 methods

1. Using LED on Volvo diagnostic unit in engine compartment to display codes. (Scheme 1)
2. Using Volvo Scan Tool (998-8686 ) connected to Volvo Data Link Connector (DLC) in engine compartment.
3. Using a generic scan tester connected to On-Board Diagnostics II (OBD II) Data Link Connector (DLC). DLC is located in center console in front of gear shift lever. see scheme 3

On-board diagnostic unit for retrieving codes is located in right front of engine compartment. Diagnostic unit is equipped with an LED indicator, activation button and function select cable.

Diagnostic unit output socket No. 2 is used to retrieve 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 ECM memory are read by observing LED flashes.

All fault codes contain 3 digits (example: 2-1-3). Since codes have 3 digits, each code requires 3 series of flashes. A 3-second interval separates series of flashes. (Scheme 2)

Scheme 1

Scheme 2

Volvo Self-Diagnostic System

System is capable of self-diagnostic functions through the use of Volvo diagnostic unit in engine compartment. System has 3 test modes. Test mode No. 1 is used to display and erase codes. Test mode No. 2 is used to verify operation of system components. Test mode No. 3 operates components in a certain order. Access to diagnostic system is provided by socket No. 2 on diagnostic unit with ignition on.

Test Mode No. 1 (Displaying Codes)

1. To retrieve codes, open Volvo diagnostic unit cover (located in right corner of engine compartment) 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.
2. 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.
3. If a fault code is retrieved, refer to the «TROUBLE CODE DEFINITION»(ref-12933-S16043138392000122900000) table under TROUBLE CODE IDENTIFICATION. 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.

Test Mode No. 1 (Erasing Codes)

1. Codes can be erased only after all DTCs have been displayed and first DTC has been repeated at least once. To erase DTC, turn ignition on. Press test button on Volvo diagnostic unit and hold for more than 5 seconds. Wait for LED response.
2. Press button again and hold for more than 5 seconds. Turn ignition off and on. Start engine. All DTCs will be erased and all adaptive values reset.

Test Mode No. 3 (Operating Components In A Certain Order)

This function is activated by briefly pressing test button on Volvo diagnostic unit 3 times. Electronic Control Module (ECM) will respond by activating listed components in order. This sequence is repeated twice. Test mode No. 3 cannot be activated while engine is running. The following components are operated.

1. EGR vacuum controller.
2. Turbocharger (TC) control valve.
3. EVAP valve.
4. Engine cooling fan, low speed.
5. Engine cooling fan, high speed.
6. Injectors.
7. IAC valve.
8. A/C relay.
9. RPM (tachometer indicates 1250-1500 RPM).