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check engine - code 24 - speed sensor circuit ??; what causes a "vss code" (24) ?
Topic Started: Aug 14 2009, 11:31 PM (2,246 Views)
pancakeron
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Hi... We took a drive down to Santa Cruz this evening, in our 93'vert, 1.0L, 5spd...
on the way i had some heating issues... mainly when going uphill at approx 3k rpms...
was able to turn on the heater and blower to relieve the engine heat...

I also noticed the check engine lite came on a couple times... turned off by itself...

When we stopped for dinner, I checked the coolant level and oil, both were fine, no noticible loss...or change in consistency, color, etc..
I plugged the diag plug with a spare fuse, and get a "24" code reading... vehicle speed sensor circuit"...

The only thing I can think of (that maybe) causing my overheating issue would be the timing
being advanced too much(?)... I believe I last set the timing at 9-10 degrees btdc...about 4-5
degrees advanced from factory spec (5 deg btdc)

As we are away from home, I don't have my manual with me, so I was hoping
someone here maybe familiar with this code and it's causes, etc...?

Thanks for any info, help and/or etc....!
...
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crankcase


Check that your radiator cooling fan is comming on. An expanded or contracted upper or lower radiator hose whould be something to look for to indicate an obstruction in the cooling system. Something blocking air flow from comming in through the radiator could cause overheating, then there is always the thermostat.

I would first concentrate on the fan.
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Bad Bent
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Facetious Educated Donkey

I found: Code 24 Vehicle speed sensor signal showed less than 3 MPH for 2 seconds when engine speed was greater than 3000 RPM and transmission has not been in park or neutral for more than 4 seconds. Or vehicle speed goes from above 18 MPH to 0 in less than 2 seconds without applying brake. This code can only appear when the vehicle is in motion, if it appears when the car is not in motion, ignore it. Check ECM connections.

The engine temperature is going to rise a little, 2-3-4 needle widths when climbing. The fan may not have come on like crankcase said, perhaps the Coolant Temp. Sensor, Thermostat and/or radiator cap may be going bad.

The last two things you replaced or repaired were?

Climbing out of San Jose is a serious climb, I'd heat up a lot also. My Geo goes from 10 o'clock to almost 12 o'clock on the gauge, on really long climbs. Did it go back to normal on the coast? If so I wouldn't worry, just be aware it will do it again on the way back.
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Since1990
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Rather than start a new thread...


I was on my way downtown this afternoon when I noted a check engine light on the convertible (it is an absolutely beautiful day here, btw). No running issues. The light was still on through the drive home and when I got around to checking it.

This is actually the first time I've gone looking at DTC codes on a Metro, oddly enough. I bought an OBD II scanner a couple of years ago (never used it) for my 98, but the 92 is OBD I so finding it - a task in itself - did not resolve my problem. Good thing the code can be read directly.

Code 24. Vehicle Speed Sensor system.

Okay...

The speedometer reads fine so I will assume the cable is properly attached.

I reset the ECM (unplugged it for a minute) and in a subsequent drive the light remained off. I will guess it's an intermittent problem. The light came on once before, a couple of months ago, but went out within five minutes.

The speed sensor itself is a switch that opens and closes four times for every revolution of the speedometer cable. This triggers either a high (12V) signal or a low voltage signal in the ECM, which can be read on a Tech 1 in either mph or kph (wish I had a Tech 1!). If either the high or low signal remains unchanged for more than four seconds the ECM sets code 24. (According to the FSM - bought on ebay - which I am REALLY GLAD to have!)

First (most probable) guess is a loose ground on/for the cluster. A loose screw/bolt in a 22 year-old car is certainly plausible. I doubt the VSS itself is at fault, which is comforting since the sensor appears to be an integral part of the cluster. There's also the relevant wire from the cluster to the ECM but this is an unlikely culprit since that part of the wiring is better protected from the elements and shouldn't have corrosion issues. The ECM (or conceivably the ECM ground) may also be at fault, in which case I should expect random codes to appear and/or the vehicle to stop running.

It does raise the question: can the car run if it doesn't know how fast it's going? Does it care?

Has anybody else looked into this code lately?
Edited by Since1990, May 22 2014, 11:26 PM.
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clarkdw


Lube your speedo cable. DTC 24 can be set by a sticky speedo cable.
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Since1990
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clarkdw
May 22 2014, 11:51 PM
Lube your speedo cable. DTC 24 can be set by a sticky speedo cable.
I read that too but shouldn't I expect the speedo needle to fluctuate if the cable were sticky? I've had vehicles with bouncy speedometers. The Metro speedometer reads steady. Also, the light came on while on the highway: hard to believe the cable stopped turning for four seconds at cruise speed.
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clarkdw


My Mpguino speed readout fluctuated a lot in cold weather till I lubed the cable. No indication of it on the speedometer and never had a VSS trouble code but the FSM says it so there must be some rationale to their statement.
Edited by clarkdw, May 23 2014, 01:43 PM.
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Since1990
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On a drive today I hit a bump and the light came on again, stayed on until I shut the car down. Went out when I restarted it and no further incidents on the way home.

I might order one of those bluetooth OBD readers on the market now (I've been waiting for an excuse), and see what the ECM is registering.

I'm still curious as to whether knowledge of vehicle speed has any bearing on how the ECM controls engine function. It would seem to be useless information given that there are five speeds (six if counting reverse) at which engine operating conditions can be identical.

Really, the only plausible uses that come to mind for a VSS is in sophisticated braking systems (ABS and traction control come to mind), electronically-controlled automatic transmissions, and post-mortem analysis of crash data (law enforcement can use this to determine how fast the car was going after the fact).
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myredvert
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myredvert

Since1990
 
Really, the only plausible uses that come to mind for a VSS is in sophisticated braking systems (ABS and traction control come to mind), electronically-controlled automatic transmissions, and post-mortem analysis of crash data (law enforcement can use this to determine how fast the car was going after the fact)... I'm still curious as to whether knowledge of vehicle speed has any bearing on how the ECM controls engine function...
It's always interesting to see what an intelligent mind can imagine with when it's not slowed down by details like the actual engineering logic diagrams for PCM functions. ;)
clarkdw
 
...but the FSM says it so there must be some rationale to their statement.
^^^This^^^. In my opinion, the "plausible" uses for the VSS are every single one of the uses the design engineers programmed the PCM to use it for whether I'm aware of them or not. The design engineers used it, so it must not have been useless to them. Without access to actual engineering details there's no telling how much it is actually used. To me smart money says outside of those basic descriptions of functions where the FSM does mention VSS, it's likely used more than we can know from having only limited information from extremely simplified documents like a service manual. :news

At the very least according to the FSM, VSS is used as a parameter that the PCM uses to schedule injector operation, the shift indicator, and although I'm not very familiar with which ones offhand, it's reasonable to assume it's part of the logic to set various DTCs. :whistle
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