Closed Loop Control Quick Check

If you suspect that the ECM is not responding correctly to the oxygen sensor signal, a quick check of the closed loop system can be made by artificially driving the system rich or lean and observing the corresponding change in closed loop fuel control. This check can be performed as follows:

• Temporarily remove the fuel pressure regulator signal hose and plug it, to create a rich condition. The ECM should respond by commanding the injectors to lean the mixture.

• Temporarily create an intake manifold vacuum leak to make a lean condition. The ECM should respond by commanding the injectors to enrich the mixture.

On vehicles with serial data, changes to 02S signal, fuel trim, and injection duration can be observed using the Diagnostic Tester.

CAUTION: When performing this type of check, avoid prolonged mixture imbalances (both lean or rich) for any extended length of time, as this may cause the catalyst to overheat and permanently damage the converter.

Closed Loop Control

Quick Check

Vacuum Sensing

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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