When is a car sensor just a sensor & when is it not?

B0bbyEwing

So an issue with my car could've been one or both of two things. Currently ruled out the EGR valve so on to the crankshaft sensor.

Slight debate over which one is the correct one for the car but most feedback came back as 036906433E.

Hopping on eBay & filtering the results for UK based only, the listings start at £12.99 and varies way up to £58.

The part from AVS is listed as Hella £21.42, probably + shipping but still cheaper than £58 & dearer than £12.99.

Now obviously if I go to the main dealer & say give me the suitable sensor for that car, it'll be the one that's for that car … at a premium cost & we know that that's not the only working option.

Now I'm going to hazard a fair guess that I don't need to spend £58 in order to get a working part but with such a range, is there any particular reason as to why not to buy the cheapest at £12.99?

Because in my mind it should be perfectly fine, especially when it's allegedly Bosch, so not even unbranded. Just the varying prices make me wonder - why & perhaps there's a reason not to buy the cheapest.

forgotmyname

Depends if the cheapest one is really to the OEM spec. Guy on YT is a specialist in electricals one of those places the garages
and even the main dealers send the car to when they fail to repair them.

I think it was a Renault and it had several parts including a new turbo and several sensors and still the car did not run properly.

He checked the spec of a part and found the voltage range to be incorrect, ordered one from a main dealer and they sent the
same aftermarket part that did not work. He sourced a genuine manufacturers part and the problem was solved.

So this car had been to a garage and a main dealer and none of them fixed the issue, imagine the bill they gave the owner
for all the failed attempts.

B0bbyEwing

https://forums.moneysavingexpert.com/discussion/comment/81952347#Comment_81952347

Yeah I've heard that with sensors before.

Suppose it just comes down to a maybe it will, maybe it wont, which is unfortunate.

As I say, the £12.99 is allegedly Bosch & if so then you'd think that in theory it should be A-ok but as in the case you mentioned I'm sure they didn't use mickey mouse sensors & yet it didn't work.

So there's a chance it may well be the cause of my trouble but the part bought may just be inferior for whatever reason & I'll be scrapping the car for £12.99 in a way.

Hopefully that's not the case & it fixes it.

Ibrahim5

There are often really good pictures on the internet. If you can get a good picture of a genuine one you can often work out who has made it. It is often Bosch for VAG cars. Some eBay sellers seem to charge silly prices. I often wonder if people think that they will get the best by paying the highest price so some eBay sellers just charge more to get these buyers hooked.

B0bbyEwing

https://forums.moneysavingexpert.com/discussion/comment/81952542#Comment_81952542

That's my thinking.

Years ago you used to be able to get a deal. These days everyone seems to expect top dollar for crud. It's like - I hear things are expensive these days so let's take the £15 I think the item is worth & ask for £35 instead.

I've ordered numerous parts from AVS before today & never had a problem. They only have 1 crankshaft sensor listed & it's Hella so that's what I've bought, just on eBay for cheaper.

Car isn't really in the condition to be spending big money on it. It'll either work or it wont. Hopefully it does, I can get it MOTd & then I'm back on the road with my own car again. If it doesn't then it gets listed for sale as S&R & if that returns nothing after a month or so then it gets scrapped & I buy another car. Petrol this time though.

Goudy

A "genuine" sensor will be branded the same as the car manufacturer brand.

An OEM will be made and branded by the company that made the sensor for the manufacturing car brand. This might have come from different companies though. It's usual for the car factories to use one or two different suppliers for certain parts.

An aftermarket sensor is just a copy made by someone else, it may or may not be made to the same standard and have the same quality controls.

Your basic car sensor takes a 5v feed from the cars ECU and alters it one of a few different ways depending on what type it is.

It then returns that altered signal back to the ECU.

There are only a couple of other sensors on a car that work differently, mainly the O2 sensors but for things like the crank, it will effectively chop this 5v signal up and return that chopped up signal back, the frequency of that chopped up signal will be the speed of the crank.

This means with a bit of thought, the sensor (and it's wiring) can be checked.

First off is it getting the 5v feed from the ECU? A multimeter is handy for this, check the terminals at the loom end of the sensor plug with key on. One terminal will be the feed voltage, one the return signal and the other the ground.

Next is what is it returning? You might need some sort of diagnostic tool for this or an oscilloscope. What is the signal like from that sensor back to the ECU with the engine running/cranking? Is there a steady RPM signal or a reading on the oscilloscope that shows a reliable crank speed pattern.

Don't forget, the sensor is at the middle of a line of wiring loom, from and back to the ECU and that is prone to faults like breaks, splits and corroded or damaged connectors, it's not always the sensor at fault.

I've lost count of the number of cars I've looked at that have had "sensor problems" and new sensors fitted to later find there's a fault in the wiring.

B0bbyEwing

Thanks Goudy. Yeah I'm aware it may be the wiring. Especially on a 21yr old car with constant hot-cold cycles & this awkward location it's in.

Hopefully the weather behaves at the weekend & I can have a see.

Goudy

If you have a multimeter, you can easily check the feed voltage with the ignition on and also the ground on the loom to the sensor.

You can then set it to Ohms and check the resistance of the sensor. Obviously OL is open and something is broken, but I would expect to see over 200 ohms on a sensor like this.

The signal is a little harder, you won't get anything coherent on a multimeter, but with a basic diagnostic tool you should be able to read the crank speed even if it won't start, the starter should spin the crank up to around 200-300 rpm with a good battery.

Now if the ground wire is iffy, that's easily sorted.

If the feed or signal wire is iffy you need to find the right pin on the connector to the engine ECU and jump it with a piece of wire to test it.

If it all checks out, I think you need to look elsewhere

Mildly_Miffed

An engine bay is a really hostile environment for electronics.

Heat.
Vibration.
Water.
Oil.
Electromagnetic interference.

…and people moan when an OE sensor "only" lasts 20 years.

Put that part number into Autodoc, Bosch for £23, so your Hella £21 is about right.

Goudy

There are a couple of models I've come across that end up with wiring faults on these circuits mainly due to age.

It's normally either the ground or the live feed.

They start with one feed and ground wire on each loom branch and then split off to individual sensors in that branch, so you end up with several Y type joints inside the loom at various points. (then of course all the returns are individual) .

These joins start becoming loose and brittle and eventually fail.

As these are very low load wires, they are just thin cooper strands rather than multi stranded and wound wires to save weight and over time they get brittle.

I'm not saying all sensors are totally reliable, but if suspected it's worth doing a couple of basic checks before condemning one.

B0bbyEwing

https://forums.moneysavingexpert.com/discussion/comment/81953073#Comment_81953073

tbh with you, I'm extremely basic on mechanics but not even as adanced as exttremely basic when it comes to electronics.

I did use a multimeter when installing a dash cam but I'm not sure of much beyond that.

I do have genuine VCDS but not fully sure in how to use it to its potential.