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1992 Toyota Previa problems
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July 1, 2010, 1:48 AM
I recently bought a 1992 Toyota Previa van and it has some issues that I am having a hard time finding the answers to. First, I cannot find an online list of the fault codes retrieved from the check engine light. Codes: 21, 25, 26, and 43. Second is an odd transmission issue. There are times when first driving the vehicle or when you come to a stop, that the transmission seems like it is stuck in overdrive. It just doesnt want to go. It does shift just fine manually however. If you push it when it doesnt want to go, after a few seconds, you can feel it drop into 2nd then 1st or 3rd to 2nd and the "O/D off" light will flash off and on. Can somebody please help?

July 1, 2010, 12:33 PM#1
Though its a Chrysler site, I think the codes from work on Toyotas too. I think they're standard SAE codes.

21: Oxygen sensor reporting too lean or too rich after 2 – 12 minutes with temp over 170° and RPM above 1500 (heated O2 sensor failure)

25: Air Idle Speed motor shorted or voltage out of range

26: engine injector driver circuit one shorted or open OR injector peak current not achieved

43: Ignition coil driver circuit open or shorted

July 2, 2010, 6:30 PM#2
Thank you very much for the speedy reply. i found the info very helpful. As far as the transmission issue is concerned, I talked to a transmission shop and they said that if the tranny shifts and feels normal during manual shifting, than the problem lies in the electronics for the tranny. They told me that the codes could be retrieved but could not (or would not) tell me how. Do you by chance know or know where i could get that info from?

July 8, 2010, 5:32 PM#3
To retrieve the stored codes off the OBD on the car - you need to short the diagnostic pins on the port under the hood. They make a special short pin to do this, or you can fashion your own out of some wiring or even a paperclip.

Here is a link on how to do it -
- basically after the pins E1 and TE1 are shorted, the ECM will fall into a diagnostic mode and "flash" the trouble codes through the check engine lamp. They do make OBD-I code readers, but they wont tell you anything more than what this "free" method with do. Different circumstance with OBD-II systems (1996+ vehicles) as the information is too complex to be flashed by the onboard system.

As for the trouble codes, they are more or less universal, but just in case - these are the ones listed for Toyota specifically:

21 - Oxygen Sensor Fault

25 - Air-Fuel Ratio Lean

26 - Air-Fuel Ratio Rich

43 - Starter Signal Fault

For the transaxle, I agree with the mechanics, likely to be an issue with the shift solenoids or the lockup converter. First thing I would try is to do a full transaxle drain and refill, pan drop and cleaning, replace transaxle filter, and a good lookover the connections to the solenoids. Transaxle flushes are only OK if they use the machine that connects directly to the pump - the ones that require the transaxle pan to be removed. The cheaper machines that connect to the cooler lines can cause deposits and grit to be circulated through the transaxle, potentially leading to more problems/make things worse.

Not sure when those codes were stored, but this seems to point at electrical gremlins. If there was any recent electrical work done to the car - new radio, alarm system, aftermarket electronics, etc. - I'd look into those installation to make sure that no other wiring was damaged in the process.

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