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Eric, Automotive Repair Shop Manager
Category: Toyota
Satisfied Customers: 32349
Experience:  20+ yrs. experience as repair shop manager and technician.
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2002 Sienna: dealer says..ecm..the catalytic converter and o2 sensors

Resolved Question:

My 2002 Sienna is giving a p0420 code, which means the catalytic converter is performing out of spec. The dealer says I need a new ecm for about $2000 and that the catalytic converter and o2 sensors are ok. Is it possible to get a new ecm myself and replace the "defective" one myself. And would that really solve my problem?
Submitted: 7 years ago.
Category: Toyota
Expert:  Eric replied 7 years ago.



This is actually a known problem with Toyota and they have issued a Technical Service Bulletin on this issue. It is covered by an 8yr or 80,000 mile warranty and does require replacement of the ecm, along with new software programmed into it. Because the software is proprietary, it can only be done by a Toyota dealership. Not even us independent shops have access to this software.




October 19, 2005

M.I.L. "ON" DTC P0420


'01 - '03 Sienna



Under certain driving conditions, some 2001 - 2003 model year Sienna vehicles may exhibit a M.I.L. "ON" with the following DTC:

^P0420 (Catalyst System Efficiency Below Threshold [Bank 1])


The Engine Control Module (ECM) (SAE term: Powertrain Control Module/PCM) logic has been modified to improve this condition.


Repair Procedure

1.Verify DTC P0420 with the Diagnostic Tester by referring to the Technical Information System (TIS), 2001 - 2003 model year Sienna Repair Manual: Diagnostics: Engine: Pre-Check.


2.Replace ECM (PCM). Follow the Repair Manual ECM replacement instructions. Refer to TIS, 2001 - 2003 model year Sienna Repair Manual: Introduction: How To Troubleshoot ECU Controlled Systems: How To Use The Diagnostic Chart And Inspection Procedure.


3.Perform the following steps to confirm that the vehicle is repaired.


A.Reset the Readiness test by using the "Clear DTC" function on the Diagnostic Tester.


^To clear the DTC, refer to TIS, 2001 - 2003 model year Sienna Repair Manual: Diagnostics: Engine: Pre-Check.


B.Perform Readiness Monitor Drive Patterns for Catalyst Monitor 02S type and AF Sensor type. Refer to TSB No. EG003-02, "Readiness Monitor Drive Patterns," procedures: Catalyst Monitor (02S Type) and Catalyst Monitor (AF Sensor Type).


C.If a DTC is set during the above drive patterns, refer to the Diagnostic Trouble Code Chart in TIS, 2001 - 2003 model year Sienna Repair Manual: Diagnostics: Engine: Diagnostic Trouble Code Chart. Test drive the vehicle to confirm normal operation.


4.If NO DTCs (pending or current) are stored, the repair is complete.
Eric and 2 other Toyota Specialists are ready to help you
Customer: replied 6 years ago.
Ok, I'm finally ready to bite the financial bullet and replace the ecm (89661-08070) on my 2002 Sienna. The 2005 TSB states to replace it with 89661-08071, but I see that Toyota now shows a 89661-08072 as the current part. What is the difference between these two units? Can I use either one. If I install the new ecm myself, do I need to reprogram the computer to recognize my transponder keys? Does the Toyota dealer have to be involved in any flashing or reprogramming if I use the newer part?

Expert:  Eric replied 6 years ago.

give me just a few minutes to look up and see if there are any substantial differences between the 2.

Expert:  Eric replied 6 years ago.

the ecm has been further updated on its software and you need to use the newest part in order to not have any software issues. the toyota dealer will have to program it with your VIN code and mileage. No way around that.
Eric and 2 other Toyota Specialists are ready to help you
Customer: replied 6 years ago.
Thanks for the info. I'll work on getting the newest ecm (89661-08072). I can order a new one on the internet for a few hundred less than at my local toyota shop. If I install the new ecm myself, will the car be driveable so I take it to the dealer, or should I drive it there with the old emc and let them take care of things?
Expert:  Eric replied 6 years ago.

you can take the ecm into your dealer, have them do the programming and then install it. It doesnt have to be installed first
Customer: replied 6 years ago.
I called my local toyota dealer, and the service person said they could program my new computer for $85 if I brought it in. So I brought it in a few days later, and I was told it had to be installed to be programmed. They wanted over $300 to install it even though I already had the panels off. So I just went home and installed it myself. Took about 15 minutes. The sienna seems to run fine as it is. What do I gain by taking it back to Toyota and letting them "program" the new ecm? I don't mind doing it if there is a benefit. Maybe I'll find something that isn't working right in a few days, but right now all seems good.
Expert:  Eric replied 6 years ago.

the new came programmed, so no need to take it in unless you experience any problems. about the only thing to gain now would be if there were any new updates not programmed into the computer at this point