Emissions - Correct Diagnosis of Emission Control Parts

91mitsubishi04

NO. TSB-91-17-002

DATE March, 1991

MODEL All


SUBJECT: "NO PROBLEM FOUND" PARTS

(CALIFORNIA DEALERS ONLY)


PURPOSE

This bulletin is to emphasize the importance of correct diagnosis of emission control parts.


BACKGROUND

In 1990 the California Air Resources Board (CARB) announced that vehicle manufacturers must submit a report to the CARB whenever the failure rate of any emission control part installed in California equipped vehicles, such as oxygen sensors, coolant temperature sensors, throttle position sensors, etc., exceeds 1% over the life of the emissions warranty. If a component has a failure rate of 4%, the vehicle manufacturer must initiate a recall.

All California equipped vehicle emission parts removed under warranty by Mitsubishi Motors Dealers are returned to our Warranty Parts Return Center after a Parts Return Request letter is sent. From there they are sent to the vehicle manufacturer for extensive testing. Outlined below is a summary of a few tests.

Coolant Temperature Sensors: These sensors are tested for resistance at various temperatures. They are also tested for shorts to the housing.

EGR Valves: These are tested for diaphragm leaks, pintle sealing, and exhaust gas flow rate.

A VERY HIGH percentage of returned parts tested have been found to operate within acceptable service specifications.

Although it is possible that under some conditions these off-vehicle tests may not identify the exact malfunction as when the component was installed in the vehicle, this is a rare exception.


Please take the following steps to ensure that the suspected failed emission part(s) are thoroughly tested before considering replacement.

1. When the self-diagnosis codes indicate a failure such as a Coolant Temperature Sensor, remember this includes not only the component but also the component connector, intermediate harness connectors, and ECU connector.

2. When checking the oxygen sensor with the Multi-Use Tester, the sensor must be at operating temperature (600~ F or higher). Oxygen sensors do not develop reliable voltages when below 600~ F.

3. It would be helpful to add a tag to the replaced parts showing your test readings.


If you have any questions please contact your District Service Manager. If an emission control part has failed during the applicable warranty period, definitely replace it ... it is essential that the vehicle operate to the correct emission standard to protect the environment. On the other hand, do not arbitrarily replace a part if your test procedures indicate that the component is operating within factory specifications.





TYPICAL SENSOR OPERATING RANGES