Speedometer not working

[SteveSarre]

Hi all,

1998 V70 T5 Auto

Car has generally been running fine.

Started the car this morning and the Speedometer is not working.
Service reminder light is flashing once per second.
RPM and coolant temperature indicator are working.
No fault codes (as read by Torque).
No mpg readout.
No ABS warning light is on.

I haven't been able to test the ABS yet because I couldn't find a slippery patch of road and didn't want to cause a pile up. ABS module was replaced (new old stock) about 2 years ago.

I have disconnected the battery and pressed the brake pedal, and reconnected the battery but that didn't make any difference.
I will leave the battery disconnected again overnight and try again in the morning.

Has anyone experienced this and have any ideas, or recommended steps to diagnose?

I have recently done various things, which of course may be related (or not), which I will write up and post here a bit later this evening.

Thanks
Steve

[Luxobarge]

First thing that comes to mind is front left ABS sensor, as this is where it gets the road speed signal from, but it's odd that there's no ABS warning light on, because if there's no meaningful signal then I'd expect the ABS module to see this as an error. I think you're on the right track in wanting to check the actual operation of the ABS system, that's what I'd do, but as you say it needs to be on a safe but slippery road.

[SteveSarre]

Some more background, which may or may not be relevant.

Yesterday the car ran fine and last night I disconnected the plug to the idle air control valve, and plugged it into (but didn't fit) a used spare that I had, because I wanted to test it (for use on another car).
The used spare iacv seemed to operate correctly, so I removed the old one (which I found to be gummed stuck) and fitted the used spare.
At some point I noticed that the lambda light had come on, but I assumed that had been because at some point I had had the ignition on with no iacv connected.
Disconnecting the battery, and pressing the brake pedal cleared the lambda light.

Then I had the "no speedo" problem this morning. The car starts and runs fine.
No fault codes, but the service reminder light is flashing.

I'll go back out now and check whether Torque can connect to the ECU and see what it lets me monitor.

Also over the last few weeks, I have been using Torque to closely monitor coolant temperature (which led me to replace the thermostat). One problem solved.

And I had also been monitoring the long term fuel trim, and o2 sensor readings, throttle position, and boost, and had noticed that every now and again one or more sensors would flick either to a very low or high value or would indicate "no data".
So I suspected a bad connection somewhere but don't know where to start looking.

If its not too cold tomorrow, I could refit the (cleaned) old iac valve, just to rule the used iacv out.

I will also test whether the ABS kicks in if I lock the wheels.

Some googling points towards the ECU. Anyone any experience of that?

Thanks,
Steve

[SteveSarre]

Well, I disconnected the battery again at about 20:00.

Then at about 21:15 I went out again to see if ABS and Torque works, and now everything works!

Now the speedo works fine, no flashing Service reminder, and the ABS works.

Slightly puzzled but pleased that things are working.

It may be that the erratic Torque readings are down to my mobile or my OBD2 adapter (I have a couple of mobiles and couple of the OBD2 adapters, and I think that one of those is faulty). I will try to pin that down.

So overall, there seems to some difference between a quick battery disconnect (and pressing the brake pedal), and a longer battery disconnect.

HTH
Steve

[acshortt5]

Could be the electrical part of the ignition, it can do wierd things. If it happens again try gently moving the key one way then the other a small amount in the ignition to see if it fixes it. Not expensive or difficult to replace.

[SteveSarre]

Hi Andrew,

I hadn't thought of that. If it happens again, I'll give it a wiggle.

I'll also look out a spare ignition switch back to keep on hand.

At Skandix 55 euros Volvo part number 9447804

I'll look in the shed. I'll need it one day.

Thanks,
Steve

[Clogs]

If the speedo dies and no warning lamps come on, there may be a loose connection in the ABS control unit. Switch off ignition and open the ABS unit (remove air intake filter housing to access the unit better as it's a bit tight to get at), and open it up, check the connecting plug is not corroded, and if that doesn't do the trick, try wedging some old credit cards or visiting cards between the unit. If that does the trick, then it's likely the solder joints need redoing and that involves removing the back of the unit and breaking the seals. See previous posts on this issue.

[SteveSarre]

Hi Clogs,

Yes I have had that problem on other V70s, so I know the symptoms and the cure.

I might be wrong, but I think if that had been the problem, I would have got an ABS light, and it wouldn't cause the flashing service reminder light.

Still not 100% sure what caused this, so I will keep an eye on it and post here if I learn anything more.

Thanks,
Steve