Fault code 24

[tom50]

My cavalier seems to have developed a new fault where the engine will intermittently lose power under load briefly before resuming normal running ,
it has also when idling reduced engine speed causing it to run very lumpy for around 30 secs to 1 min before idling normally again , if i pressed the throttle whilst i running slowly There was intermittent acceleration in a on /off cycle , eventually it will clear and run normally again, it did store a error code of 24 which would indicate a speed sensor,
My cav has a cable from gearbox to the speedo in the dash, so no speed MPH sensor present on my model , IMO i think it's likely to be the TPS, or the CRANK sensor if you add in that older run on problem the car has ABS , but that wouldn't affect the engine

Just thought i would pick the brains of those with more knowledge than myself

[ilovedmymantas]

This might be helpful viewtopic.php?f=15&t=13780&p=143803&hil ... or#p143803

There's a speed sensor in the instrument cluster, it may be dampness has crept in at this time of year and affected it.

[tom50]

Very possible with the leak of water into the boot, and driver's door seal being knackered which on a frosty night will cause the alarm LED to blink rapidly which at a guess will be one of the ultrasonic Sensors getting damp too

Just one other thing, can the car live without this speed sensor?,
if all it does is increase the sound output, Should you have a radio that has this feature , i have the fitted radio which the lcd display is Goosed and therefore i'm unable to enter the code properly ,.so it's no longer even used

And the car is a MANUAL not auto

[Robsey]

You will find a thousand and one faults being kicked up by the huge amounts of wind and rain recently.
And condensation of course.

The only 'free' things you can do is...
Disconnect the car battery for a while to reset the ECU and fault log history.
It will also cause the ECU to go back into learn mode when you reconnect the battery.

I would then give it a good run with the cabin heating set to full, in a bid to dry stuff out.
I tend to drive quite briskly for the first 15 minutes or a similar number of miles, which should be enough for the re-learn phase to complete.

If you are still getting your speed sensor fault, then we can assume that damp is not the only issue.

You could check that your ECU is clean and dry as corrosion hidden at the base of the A pillar could allow water to leak in above the ecu.

My usual ritual if I have anywhere exposed is to ensure that any connectors are clean, dry, and securely fitted.
For moisture prone areas, I smear on a thin slither of vaseline onto the connector pins to slow down the ingress of moisture or corrosion.

[Robsey]

The speed sensor depends upon your model year and engine.

The speed sensor for 1990 to 1994 cars is to convert the mechanical speedo cable revs into a square wave signal, which is used for the speed dependent volume control, board computer, electric sunroof, and dual info display temperature calculation. (Where fitted of course).

On 1995 vehicles the speedometer is driven by pulses from the ABS module. (So I believe).

There is a speed sensor wire on the ECU loom for all the injection engined vehicles, so I presume it is used to analyse the speed, rpm, and load for mapping purposes.

[tom50]

Mine is a 1995 ECOTEC 2.0.16V GLS no electric sunroof or duel info only clock and outside air temp unless that is what you meant by duel display and it has a speedo cable from gearbox to head of speedo I can think of a way that may show how the speedo is controlled ,if electronically then when moving coast turn ignition off, if speedo is electric it will stop working, if cable it should continue to work unless the speed sensor is inside the speed it's self looking at pictures of the PCB for the cluster lights there are 3 big tracks that go where the speedo would fit by the looks of it ?

From a bit of research, i found some speedos have something like this attached to the back of the speedo clock , but some have it built in on the circuit board of the instrument cluster https://www.ebay.co.uk/itm/134058436218 ... 6a3d15313b

ACCORDING TO THIS , https://www.vauxhallownersnetwork.co.uk ... eed.68199/ But the idle speed when stationary is in normal range it is around 1100rpm when coasting or slowing and soon drops to normal once stopped ,

it has done this for ages, the new issue is different to the other posters issues, the recent symptom which is intermittent and happens whilst under load or idling where under load i randomly loose all acceleration for like 2 seconds then it returns again, causing a kangaroo effect, When idling with foot off peddle, it will idle under the 700-775rpm, at a juddering 200rpm less,

if i press the accelerator it will either not respond, instantly or stall,If i hold the pedal at the same level i observe normal acceleration /power or nothing and it will fluctuate on/and off for a few mins or shorter period, then clear by it's self, the only times the ELM has is very recently, I switched the ignition off and started the car, to see if it would remain on, and it did, but as i reversed out of the parking space it cleared MIL light , I did have full power whilst the mil was lit, no derating from revving whilst stationary

[James McGrath]

On 1995 vehicles the speedometer is driven by pulses from the ABS module. (So I believe).

This is certainly the case on my 1995 Cavalier. I had a faulty ABS sensor once and it caused my speedo to stop working while I was driving!

Personally, I don't think a speed sensor could cause such issues. I recon that code is just stored in your ECU and not a current problem.
Disconect the battery for a few hours, that will reset the ECU and any fault codes. Then drive it around for a bit and see if the code comes back.

If it doesn't, start some good old fashioned diagnostics. Look at fuel pressure, ignition, idle control valve etc. There are lost of things that can go wrong on Cavaliers that will never bring up a fault code.

[Robsey]

The nearest issue I can think of, affected my C18NZ many years ago.

I had a vacuum leak in my MAP sensor, allowing too much air in.
The Oxy sensor continuously triggered enrichment to counteract this.

The result was heavily sooted plugs that prevented the car from starting when warm / hot.

When cleaned or cooled, the car cranked and started okay.

Maybe I would check the condition of the plugs for sootiness.
And check for air leaks anywhere after the MAF sensor, including the throttle body or inlet manifold gaskets.

[iangsi]

I had a similar problem with my GSI turned out to be a split hose on the fuel pressure regulator, worth a look.