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.
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HOMESERVICE MANUALSBMW1994318IS (E36) L4-1796CC 1.8L DOHC (M42)REPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSDESCRIPTION AND OPERATIONFUNCTIONAL DESCRIPTIONSEMISSION CONTROL ON MODELS WITH CATALYTIC CONVERTER
1994 BMW 318is (E36) L4-1796cc 1.8L DOHC (M42)
Emission Control on Models with Catalytic Converter
1994 BMW 318is (E36) L4-1796cc 1.8L DOHC (M42)SECTION Emission Control on Models with Catalytic Converter
OPERATION
To maintain the optimum degree of efficiency of the catalytic converter, this system aims at achieving the ideal air-fuel ratio (lambda = 1) for combustion. The heated oxygen sensor is used for this purpose which measures the residual oxygen content in the exhaust gas and sends a corresponding voltage signal to the control unit. Here, the mixture composition is corrected if necessary by changing the injection timing. In the case of failure of the oxygen sensor, the Digital Motor Electronic (DME) control unit controls the system with a substitute value (0.45 V) preprogrammed in the control unit.
Since a temperature of approx. 300 C is necessary for efficient operation of the oxygen sensor, power is supplied via a relay to a heating resistor in the oxygen sensor. The relay is activated by the DME control unit.
To maintain the optimum degree of efficiency of the catalytic converter, this system aims at achieving the ideal air-fuel ratio (lambda = 1) for combustion. The heated oxygen sensor is used for this purpose which measures the residual oxygen content in the exhaust gas and sends a corresponding voltage signal to the control unit. Here, the mixture composition is corrected if necessary by changing the injection timing. In the case of failure of the oxygen sensor, the Digital Motor Electronic (DME) control unit controls the system with a substitute value (0.45 V) preprogrammed in the control unit.
Since a temperature of approx. 300 C is necessary for efficient operation of the oxygen sensor, power is supplied via a relay to a heating resistor in the oxygen sensor. The relay is activated by the DME control unit.
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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.