740 L4-2320cc 2.3L DOHC B234F (Can) (1992)
Engine Control Module: Description and Operation
The On-Board Diagnostic (OBD) System
Design and function
The on-board diagnostic (OBD) system
The fuel and ignition Systems are equipped with an OBD system with three diagnostic test modes (DTMs) to facilitate fault tracing.
The DLC is located in the engine compartment by the left hand suspension tower. Output 2 is used for the fuel system and output 6 for the ignition
system.
Faults are registered In DTM 1. If these faults are emission related a MIL is lit on the combination instrument. A maximum of three faults can be
stored at one time (the fuel system OBD system for California models can store up to 17 DTCs).
Sensor signals are tested in DTM 2. DTM 2 can be activated manually by pressing the diagnostic button twice. The control module responds with a
code if it receives a signal when the sensor is activated.
The signals to certain control components are tested in DTM 3. DTM 3 can be activated manually by pressing the diagnostic button three times. The
control module then activates the control components one by one. Whether the component is operating is ascertained by listening or feeling it.
The fuel system
The control module continually checks the following modes when the car is being driven:
-
The control module's own, internal functions
-
HO2S and fuel trim
-
ECT sensor
-
MAF sensor
-
Battery voltage
-
TP switch
-
Engine speed signal from the DI system control module
-
Speedometer signal
-
Knock enrichment signal from the DI system (does not apply to B 230 F, B 204 FT/GT)
-
IAC valve