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Engine Controls - Self-Diagnostics: Overview Suzuki Vitara I

Testing & Diagnostics ~672 words

GENERAL DESCRIPTION

This vehicle is equipped with an engine and emission control system which are controlled and monitored by the Engine Control Module (ECM). ECM has an On-Board Diagnostic system which detects a malfunction in this system and abnormality of those parts that influence the exhaust emissions. When diagnosing engine troubles, be sure to have a full understanding of the On-Board Diagnostic system.

There is a close relationship between the engine mechanical, engine cooling system, ignition system, exhaust system, etc. and the engine and emission control system in their structure and operation. In case of engine trouble, even when the Malfunction Indicator Lamp (MIL), displayed on instrument cluster as "SERVICE ENGINE SOON" lamp doesn't illuminate, it should be diagnosed referring to this flow.

ON-BOARD DIAGNOSTICS SYSTEM DESCRIPTION

ECM in this vehicle in compliance with On-Board Diagnostic-II (OBD-II) regulations, has following functions

  1. When ignition switch is turned to ON position, Malfunction Indicator Light (MIL) illuminates as a MIL bulb check-out. MIL should turn OFF when engine is running or ignition switch is turned to LOCK position.
  2. When ECM detects a malfunction which would have an adverse or severe damage to vehicle emissions while engine is running, MIL flashes (flashes only when detecting a misfire which can cause damage to the catalyst). ECM stores DTC(s) in memory. If after 3 driving cycles ECM no longer detects condition that set DTC, MIL is turned OFF. DTC will remain stored in memory.
  3. As a condition for detecting a malfunction, in some areas system being monitored by ECM, 2 drive cycle detection logic is adopted to prevent erroneous detection.
  4. When a malfunction is detected, engine and driving conditions then are stored in ECM memory as freeze frame data. For freeze frame data details and description, see «FREEZE FRAME DATA»(ref-158406-S13507330172003112500000).
  5. It is possible to communicate with ECM by using SUZUKI scan tool, or OBD-II generic scan tool which are in compliance with SAE J1978. (Diagnostic information can be accessed by using a scan tool).

Description

Engine Control Module (ECM) monitors crankshaft revolution speed and engine speed via the Crankshaft Position (CKP) sensor and cylinder via the Camshaft Position (CMP) sensor. ECM detects occurrence of misfire by calculating changes in crankshaft revolution speed, and tracking how many times change occurred every 200 or 1000 engine revolutions. When ECM detects a misfire (misfire rate per 200 revolutions) which can cause overheating and damage to Three-Way Catalytic Converter (TWC), ECM causes Malfunction Indicator Light (MIL) to flash for as long as misfire occurs. When misfire rate drops MIL remains illuminated until ECM detects normal driving conditions during 3 drive cycles. When ECM detects a misfire (misfire rate per 1000 revolutions) which will not cause damage to TWC, but could cause exhaust emission deterioration. ECM illuminates MIL after 2 drive cycles.

Engine Control Module (ECM) monitors oxygen concentration in the exhaust gas which has passed through Three-Way Catalytic Converter (TWC) by using Heated Oxygen Sensor No. 2 (H02S-2). When TWC is functioning properly, variation cycle of H02S-2 output voltage (oxygen concentration) is slower than that of Heated Oxygen Sensor No. 1 (H02S-1) output voltage due to amount of oxygen in exhaust gas which has been stored in TWC.

When engine is running, Engine Control Module (ECM) closes EVAP Canister Vent Valve (EVAP-CVV) and opens EVAP Canister Purge Valve (EVAP-CPV). If EVAP system is okay, EVAP control system pressure which was detected by fuel tank pressure sensor decreases. After which ECM closes EVAP-CPV leaving EVAP-CVV closed. If EVAP control system is okay, fuel tank pressure will then rise a specified rate.

When engine is running, Engine Control Module (ECM) closes EVAP canister vent valve and opens EVAP canister purge valve. If EVAP system is okay, EVAP control system pressure which was detected by fuel tank pressure sensor decreases. After which ECM closes EVAP canister purge valve leaving EVAP canister vent valve closed. If EVAP control system is okay, fuel tank pressure will then increase a specified rate.

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