Is the speed sensor in the diff cover?(spedo's all messed up) And what are the most common issues with the gauge cluster if there is any.

Thanks!

 

yes... and if you have ABS, the differential speedo sensor also provides the rear axle input to the ABS (its a 3 channel system, I believe, both rears are 1 channel, and each front is a seperate one).

speedometers can fail from flakey connections, bad/cold solder joints on the circuit boards inside the speedo, capacitors on the speed circuit boards leaking/failing, and there is an 'ICT' chip on them that can fail. mine (1992 740 wagon) is starting to fail where sometimes it won't read higher than 45mph, but its correct at any lower speed. then blink it starts working at all speeds again. I'm suspecting capacitor or ICT chip.

 

99% chance it's your speedometer failing, especially in 1991-92 740s and 940's are pretty bad...

 

lev, was that for me, or the OP? the OP didn't mention his model year.

I'm eventually going to pull my speedo and see if I can't get it working on the bench, using a signal generator as the speed source, then I should be able to figure out why its not working. hoping its relatively simple like capacitor, but I've heard the chip (UAF2115?) goes out too, and this behavior of being intermittent above 45 but stable below smells to /me/ like flakey chip.

edit: ooops, I have the yazaki speedo in my 92 740. meh, extra fun, http://www.volvoclub.org.uk/faq/Elec...eterRepair.htm and my symptoms sound right in line with what they say there.

 

89 with abs. And the abs light is on...hmmmm *scratches chin*
@pierce, good luck with your speedo man, I hope i dont have to do that. I felt a lil lost when i clicked on the link you posted. Haha

 

half the time or more, erratic speedo is broken wires back by the sensor.

you can do what they suggest on that page, take 15' of 2 conductor wire, like doorbell wire or whatever, connect one end to the wires where they connect to the sensor in the differential, and bring the other ends up into the cab. turn the ignition on, and tap the wire ends together like 4-5 times per second, and the speedo should read. faster you can tap, the faster you're going. if that works, then your speedo is fine, the problem is in the pickup ...

if you do have actual speedometer problems, there's two different speedometers as outlined in that article. My 92 has a Yazaki. You might have a VDO. the difference is, the trip meter... on the yazaki, each digit is in its own window, on the VDO only the 1/10ths is in its own window, the rest are in a single wide window.

that ICT/ITT/UAF-2115 chip thing I mentioned is specific to the VDO. if you know anyone who does electronics and can solder circuit boards and stuff, they might be able to fix it or show you how (you can buy the UAF2115 chip for like $30). My Yazaki, apparently the parts aren't available, but its more likely to be the capacitors, which is a common problem with LOTS of electronics, including computer motherboards and power supplies, stereo and video gear, etc.

 

oh, re ABS faults, there's a way you can read a error code out of the ABS. most of those are due to a sensor fault. oh, ooops, thats only on 1992+
Brakes: ABS
with a older car, you have to do manual tests with a volt meter.

 

Ill have to try that out. Is the sensor grounded near by? Or is it apart of the harness? Imma have to crawl under it tomorrow and check everything out. As for my speedo being vdo or....the other one.. idk ill go look though.. cause now i wanna know. Haha

 

the sensor has a shielded twisted pair, so its two wires at the sensor end. one of the wires is grounded at the speedometer end, as is the shield... its a weak signal, and doing it this way eliminates noise.

 

Ok. I believe i might be in the same boat as you... I got the same speedo. Haha ugh.

 

so what are your symptoms ?

 

Half the time it dosent work.. then it will work fine, then i hit a bump and it starts to flop around all over the place. Then i start to ignore it. I did take it through the touch less car wash yesterday and the spedo worked fine all day yesterday and a little bit of today, then i went down a dirt road.. is there a sensor for the abs around the brake rotors? Imma tear half that wagon apart tomorrow and scope out everything.

 

ok, those symptoms easily could be a loose connection where the speedo is plugged into the instrument panel, or a wiring issue out back by the sensor.

the ABS has a sensor on each front wheel, and uses the speedometer sensor for both rear wheels together. info on ABS systems here. Brakes: ABS

I'd not worry about the ABS until your speedo is sorted out. the signal for the rear wheels passes through the speedo enroute to the ABS controller, so if the speedo is outputting a spastic signal, then the ABS controller will fault and disable itself so it doesn't do something stupid.

 

Nice. Didnt notice "abs brake" was a link the first time around. Gonna check that. Thanks for the help man! Saved me some head aches haha.

 

yeah, this forums style doesn't have a good link color, its too subtle.

 

Mmhmm.

 

Fixed it! One wire just kinda fell apart, used a butt connector and bam!, Spedo's working. But the abs light is still on. The front two sensors look ok, but we didn't take them off to see how nasty they are.

 

you might have to reset the ABS controller, but no I don't know the procedure (although its probably on the 7xx FAQ site at the UK volvoclub...)

I know on the later ones, you can get a blink code out of the diag box under the hood, and this will tell you exactly what the ABS controller thinks is bad. IIRC, the FAQ said on the older pre-diag units, you have to get in there with a multi meter and run a bunch of tests.

 

I'll have to check that out. I did put that site in my fav's.