Code PO734 and CEL won't reset.

codymarshall · Post by **codymarshall** » 25 Jul 2011, 22:02

Hey all!

I have a '96 volvo 850 turbo that I've owned for about a year now.

About 2 weeks ago, I was driving on surface streets when the tranny started slipping. It slipped about 3 times in a span of a minute or so until finally the car went into "limp" mode, illuminating the blinking arrow along with the CEL.

I immediately pulled over and did some research. A google search brought me across a forum that suggested I move the gear selector up and down because it would temporarily clean the contacts on my PNP switch, and that it probably needed to be replaced.

That temporary solution worked! The transmission indicator turned off and it stopped slipping and shifted normally without going into "limp" mode, however the CEL stayed on. Sadly, despite getting a transmission flush, and having the PNP switch replaced, the CEL is STILL ON =(

The tranny has not slipped even ONCE since that day. Does anyone have any ideas why the CEL is still on (displaying the code PO734 for wrong gear ratio) even though the car is working fine and shifting normally? It's suuuper annoying and we can't seem to reset the damn light.

Post by **Juan62** » 26 Jul 2011, 03:49

On this forum, there is info on how to reset for the 850 Turbos, which are different from the S70 series.

Post by **jblackburn** » 26 Jul 2011, 08:06

You should be able to erase CEL codes with any code reader, but if it won't, disconnect the negative cable on your battery, touch the brake pedal a few times, and reconnect it. This should completely reset the computer.

In the meantime, you have just bought yourself more time with rowing the shifter. You need to do the cleaning procedure in the repair database here:
https://www.matthewsvolvosite.com/2010/0 ... -cleaning/

(Really not that difficult, even for a novice driveway mechanic).