my overdrive light on my 98 expo comes on sometimes and blinks then goes off after a while? no change on the tranny though. any ideas?

 

need to have the codes pulled when the light is on.this would help pinpoint the problem

 

I had the same problem twice with my Exp since new. Both times I shut off the Exp for a few minutes and then started to drive again without the OD light flashing again. Both times I could not detect any performance issues.

 

You couldn't, but the computer did.

You'll have to pull the codes with an appropriate reader. The el-cheapo ones won't cut it.

Steve

 

I had some problems with my OD button/light on my '99 Expy. Ended up that the wires that run inside the shift lever wore out and were shorting causing the switch not to function.

 

I am curious to know if the transmission malfunction codes are stored or if the codes can only be pulled when the OD light is flashing?

 

what code reader should i use? does autozone do this? when the light is on i can not control the od switch

 

They are stored.

The common reader used by AutoZone in the past does not support manufacturer-specific codes. Unless they have upgraded, you chances are basically hit or miss as to whether or not you will get a valid and COMPLETE code read.

It wouldn't hurt to inspect the wiring harness where if exits the shift lever. If it's frayed and one of the wires is shorting out, there can be several symptoms depending one which specific wire in the harness is shorted. One of the possibilities is what you have described. Reading codes would not be effective in identifying this particular fault.

Steve