The other day I was driving along (at high speed naturally) and my exhaust started blowing. An hour later, my speed went to zero, and my ABS and traction control lights went on, and my power steering which is speed sensitive went to fast setting. Said problem kept toggling on and off. I assumed that it was a speed sensor on at least one wheel being affected by the blowing exhaust in some way - after all all those things require a speed sensor
So I got a pipe with a hole in it replaced by a friend in the place I was who has a garage, but he didn’t have time to look at the other issue, and like I said I assumed it was probably a speed sensor.
Sadly, I had an extensive journey today after having the exhaust fixed and the problem still remains. So…
Is my diagnosis of a dodgy speed sensor probably correct? Also, what is the correct term for “speed sensor”?
Was the exhaust blowing anything to do with this or is it a coincidence the sensor problem started very soon after? I mention that I was driving at reasonably high speed because it was presumably putting reasonable stress on components and more importantly blowing more stuff down the exhaust, as the revs would have been high a lot of the time given the nature of the roads. The odd thing is that where the hole was in the exhaust (well actually the pipe basically split entirely) was about as in between the two wheels as you can get.
How easy are these things to fix DIY? Loose wiring has to be a possibility as well surely, especially given the problem is intermittent - I don’t have garage stuff myself but I can borrow them.
What kind of car do you have? A common omission on these type of questions…
On the BMWs that I’m familiar with (E36), the ASC (traction control) and ABS lights coming on at the same time and staying on generally points to a brake pedal position sensor or a wheel speed sensor, FWIW.
We can often be of much more help if we know the year, make, model, and engine size of the vehicle.
1) Is my diagnosis of a dodgy speed sensor probably correct?
Yes, it’s a reasonable guess.
Also, what is the correct term for “speed sensor”?
“Speed sensor.” Actually, there are two types: wheel speed sensors, which relate to ABS and traction control, and vehicle speed sensors, which relate to the speedometer reading.
2) Was the exhaust blowing anything to do with this or is it a coincidence the sensor problem started very soon after?
Normally it wouldn’t be related, but if it was blasting hot exhaust onto a sensor or the wiring to it then it could be the cause. Vehicle speed sensors are tyically somewhere on the transmission.
3) How easy are these things to fix DIY?
That varies a lot with the particular design. Vehicle speed sensors are usually pretty easy to replace BUT on some vehicles the access is a real bear. Wheel speed sensors are usually easy to get to BUT on some vehicles they tend to seize into their mounts and can’t be removed without destroying them.
FWIW I had a bad ABS sensor a few years ago. The design engineers judged that a low-grade bolt had sufficient strength to retain the sensor, and they were right. What they neglected to realize was that a low-grade bolt would twist apart when anyone tried to remove it after a few years of all-season service, when it was snugly rusted in place. I ended up having to drill out the remaining piece of bolt and then chase the threads with a tap. A PITA, but doable; just don’t break the tap off in the wheel hub assembly, or you’ll likely end up having to replace it along with the sensor.
Car = [[Vauxhall/Opel] Omega] | [Cadillac Catera]]* - 2003ish iirc (daft that I don’t know exact year but in UK we normally know car ages from reg plate, but this was registred in Isle of Man where you can’t and I ain’t really made sure!)
Presumably given failure mode speedo is deffo coming off same thing as wheels BUT
obviously it would be feasible for traction control and abs to also have as an input the transmissin speed - and also transmission speed would make sense in terms of exhaust location in that this is a RWD car and where the exhaust is blowing is close to gearbox in middle of car.
exhaust blowing is UK-speak for exhaust making a noise due to a hole in it.
Thanks!
*specifically this particular example is a Vauxhall Omega but they’re the same thing and put this way so most can get what it is. It used to be an unmarked police car actually, and I still drive it like it was
…obviously it would be feasible for traction control and abs to also have as an input the transmissin speed…
That is the case with this vehicle.
…and also transmission speed would make sense in terms of exhaust location in that this is a RWD car and where the exhaust is blowing is close to gearbox in middle of car.
And that is where I’d look first, rather expecting to find a somewhat melted sensor or wiring harness.
Thanks!
You’re welcome.
It used to be an unmarked police car actually, and I still drive it like it was.
Well, now if you get stopped for driving too fast you can truthfully say the speedometer is faulty.
Given the age of the car and if it’s not a diesel, it should have EOBD controls that are very similar to the ODB II system used on cars in the USA. You should have had a Check Engine Light or Service Engine Light show up on your instrument panel if it’s a speed sensor. If you have someone plug in a code reader, you may see something like a P0501 vehicle speed sensor code.
A warning about the codes and code readers: they are a place to start troubleshooting and not the final say. I know of one type of vehicle that will throw a knock sensor code and spending the $700 to change the knock sensor won’t fix a thing. Something is causing pre-detonation and that’s causing the knock sensor to go off. Same goes with oxygen sensor codes. Often changing the O2 sensor doesn’t fix the problem.
Still getting the codes read is a very good place to start.
Actually, there are two types: wheel speed sensors, which relate to ABS and traction control, and vehicle speed sensors, which relate to the speedometer reading.
