My CEL keeps coming on even though my mechanic has already replaced parts related to cat converter bank 1 code . We took it to dealer and they couldn't find anything in first inspection. We tried disconnecting battery for 3 hrs to reset ECM but that didn't work! Any suggestions would be appreciated!

 

What were the trouble code numbers?

When engine type V6 or 4-cylinder?

 

Engine 6 cylinder
code p0420
Efficiency below
Threshold bank 1

 

Does the exhaust system have any leaks? Are there any wiring issues to the AF/02 sensors or engine computer?

The P0420 code is for a converter being below efficiency. Typically this code means the converter is bad. Bank 1 is for the first converter on the rear cylinder exhaust system (closest to firewall).

Was this converter replaced and if so with what kind of part (Toyota or aftermarket)? Not all converters are the same as some work better than others. Some brands of parts work better in Toyota then others.

If parts were replaced and the P0420 code is back, what has the original mechanic done about it? It's really their job to find the problem, not yours.

Unfortunately the converters operation is monitored indirectly. This being by monitoring the exhaust going into the converter and exhaust coming out, then comparing the two. This is done via 02/AF sensors. The sensors send a signal to the car's engine computer and based on this determine if the converter is working OK.

If an 02/AF sensors has a problem, there are wiring issues or even a bad engine computer, the computer may be tricked into thinking the converter is bad.

The cars computer can be accessed from the ODBII port and real time data reviewed. This data would include the real time 02/AF sensor operation.

The computer runs several self checks before setting a code. The computer would note these checks and set a pending code until the required number of checks is computed to set a code. This data can be accessed via the ODBII port.

Would assume the Toyota dealer, who should have the correct diagnostic tools, checked everything via the ODBII port, did visual inspection and found all OK at the time. They should have also checked for service bulletins related to possible bad computers causing this problem.

The cars computer cannot be reset by disconnecting the battery. This reset is done using the ODBII tool or by correcting the problem, in which case the computer should reset itself.

As to what to do about this issue. The original mechanic should be the one working the issue. Find out what they replaced in detail and with what brand of part(s). Check for exhaust leaks, bad wiring at the sensors and computer.

 

Mechanic checked all that you mentioned and replaced both cats on the exhaust manifold with Toyota parts . O2 sensors got from parts store. He also checked exhaust for leaks, cleaned injectors and plugs changed. Only thing he couldn't test was computer . That's when we had dealer check car. They couldn't find anything with initial check either. Don't know I'm at a loss??

 

Could be a bad computer or if possible, the computer needs a reflash.

A data logger can be plugged into the ODBII port to monitor the system. When the check light comes on, the data recorded can be checked to determine what happened.