After trying every trick I know and even a few I didn't ,the fault codes on my 1990/22re will not clear... I have done everything, but the codes21 and 51 will not clear the ecu...any suggestions.. Batter d/c overnight with efi fuse pulled.. No change..

 

Have you fixed the problems that caused the codes??

With the battery disconnected they have to clear .

 

yes .. the repairs have been completed... 21 refers to the o2 sensors heater signal/ replaced with denso oe sensor.... 51 is a bit different/ neutral start switch(which my runner is 5 speed factory, tps connection (which after much checking and rechecking no fault was found in any area,then it refers to the a/c relay/amplifier( which are working as they should)... I have been over this list with much scrutiny and effort... nothing... One thing is possible I suppose... each code ultimately refers to the ecu... It makes no difference how long battery and fuse are d/c... as soon as you start the light is on with no delay... I know here where I am state inspection will not be an issue, and some say just ignore it and drive... It runs great... But I have trouble with that bc it effects the overall performance of my rig...

 

Find someone with the same ECU swap it out see if it cures the issue.

so when it comes down to it the problem is still there hence the light coming on at once.

Then you know and can find one or buy a new one if they can still be had.

i feel your pain I have one that just kills sensors

Good Luck

 

well... after a rather headscratching moment... i must admit there was one option I didn't consider that now haunts me... I replaced the downstream o2 sensor which did help some rich mixture issues and mpg went to 24, but the continued fault code for and o2 sensor heater circuit bugged me... I did not notice an upstream sensor in the exhaust manifold where one should be... removed heat shield and cannot find a wiring harness either... I know this runner has had a recent engine rebuild,by who i do not know, but it looks like it was a far cry from shade-tree work with the re-install... This appears to be a manifold from a 22r there is no port for the sensor at all, but there is a place where it would be... even more frustrating is i cannot find a wiring harness to boot... This would keep the 21 code lit up forever and then some... Does anyone have a good wiring schematic for a 1990 4runner 22re 5speed? I have found so many wires disconnected and stuff that was done 1/2 a@@@@ that it amazes me it even runs as good as it does...

 

It seems you have a hacked engine replacement or swap.

You really need to figure out just what year parts you have and go from there.

a royal mess like you said is is rather amazing it starts let alone runs.

good luck.