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Juan Crespo
Juan Crespo, Tech Trainer
Category: Car
Satisfied Customers: 1516
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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Have 99 Trooper 3.5l....no codes...monitors circuit, evap

Customer Question

Have 99 Trooper 3.5l....no codes...monitors for htr circuit, evap and cat will not clear...has been driven extensively and the correct drive procedure followed. Prior we have replaced cat o2 sensors (o2 sensors have cleared) . No trouble codes or pending codes.
Submitted: 6 months ago.
Category: Car
Expert:  Juan Crespo replied 6 months ago.

Hi there.

If the Oxygen sensor heater and catalyst monitors are not ready, the culprit is most likely a weak battery. If your battery is more than four years old, replace it and re-run the Drive Cycle. Even though your Trooper may start just fine, the PCM is hypersensitive to the slightest glitch in the battery. It will suspend the Drive Cycle if it is not happy with any aspect of battery performance and/or charging system performance.

If the EVAP monitor is not ready, verify that your fuel cap is tight and the level of fuel is between 1/4 and 3/4 full. If all the other monitors are ready, then do a couple more "cold" starts. If the EVAP monitor still has not passed or set a pending or present code, then the vehicle needs to be diagnosed with a scan tool capable of Mode 6 Diagnosis.

Customer: replied 5 months ago.
New battery installed...all new O2 sensors...new Cat...still cannot get Heater, Cat and Evap Parameters to set even when following the proper procedure in the Snap On Scanner. O2 Sensors all toggle correctly...no codes or pending codes. I believe the Heater must clear before Cat...any ideas?
Expert:  Juan Crespo replied 5 months ago.

I hate to sound pessimistic, but a new battery doesn't mean the charging system is doing what's supposed to do. That, plus the possibility of something else not allowing the monitors to execute. Do you have access to a scan tool with Mode 6 capabilities?