Hello Everybody,

I have recently been getting the following string of codes when i check them.
12, 21, 21, 55.
About a month ago i noticed that it had a single code 21 when i checked, so i changed the O2 sensor over to a different one i had laying around. Then when i went to check the codes again it read the string above. I drove it like that for a little bit to see if it would go away, however it didn't. So i put the original O2 sensor back in and drove it a bit, but the double 21 still persists. Other than the codes the truck does seem to run a little rich, but no major problems.
Any ideas?
1993 Dakota 5.2L, 4x4, Extended cab.

Thanks,
Ben

 

Are you getting a CEL? All of the listed 21 code issues have a double asterisk which means the CEL will light up.
12- battery disconnected last 50 start cycles.
55- end of codes

21- Upstream oxygen sensor voltage shorted to ground (tested after key off and at start to run) ** or
Left oxygen sensor input voltage maintained above the normal operating range. **
or
Upstream oxygen sensor response slower than minimum required switching frequency or value does not go above .65 volts. **
or
Upstream oxygen sensor heating element circuit malfunction. **
or
Downstream oxygen sensor voltage shorted to ground (tested after key off and at start to run) **
or
Downstream oxygen sensor input voltage maintained above the normal operating range. **
or
Neither rich nor lean condition detected from the downstream oxygen sensor. **
or
Downstream oxygen sensor heating element circuit malfunction. **

* Check Engine Lamp (MIL) will not illuminate when this code is stored
** Check Engine Lamp (MIL) will illuminate when this code is stored
*** Generator lamp illuminated

 

Negative on the CEL, except for the 4-5 secs when key turns on, no lights at all with engine running.