Omega Owners Forum
Omega Help Area => Omega Electrical and Audio Help => Topic started by: VXL V6 on 26 April 2022, 16:22:01
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C0040-(4) DTC - Front Right (OSF) ABS Sensor open circuit
ABS & TC lamps illuminate after a couple of miles, DTC as above, spinning the wheel while checking output on diagnostic tool shows sensor is reading pulses, I need to repeat the test when driving and see if it's still working when hot. I have cleaned the plug and socket with Electrical Contact cleaner but connections were already dry and clean and no signs of cable damage / cuts. Dont believe the reluctor ring is rusty / damaged but difficult to see without removing bearing assembly (I've never yet removed a front bearing and seen damage / rust in this area on an Omega)
Has anyone ever had a loom cable failure between sensor plug /socket and ECU? I ask because I note the loom cable runs underneath the airbox and I recently had this removed, wiggling said cable doesn't induce the fault so not sure where issue lies without further poking and prodding!
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Have you checked sensor signal at the abs ecu?
If this compares with the sensor plug test, then the wiring is probably sound. Which leaves the sensor head or the ABS ecu.
The Alabama Mumsybus occasionally throws up an ABS warning... Usually with two codes, one for rear right sensor position and one for contaminated front right reluctor ring.
The first is caused by hairline cracks in the rear sensor caused by a previous person heating out a rear bearing without first stripping the hub.
The second is suspect is caused by lateral wear in the hub as the reluctor ring is sealed within the bearing.
The Omega system is slightly different in that the magnet is on the sensor head rather than within the bearing. As such it is effectively external and prone to collecting ferrous debris.
You should be able to gain enough access to clean the sensor head with the disc off ;)
As for the ABS ecu, a known good V6 unit of similar vintage ought to be good enough to test with :y
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A meter is probably good enough to test the loom, complete with a quick inspection of the exposed bits.
On the Omega, ABS sensor faults I've seen have always been the sensor or the reluctor ring, which on the front is a new hub. ABS faults with no codes have always been a failed ECU.
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Slightly off topic, but does any one know if Carlton ABS light can be similarly diagnosed to find out why the light is constantly illuminated (once a wheel has been turned after start up)?
On some other cars I've seen the light comes and goes as you are driving, but this one is on all the time.
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Slightly off topic, but does any one know if Carlton ABS light can be similarly diagnosed to find out why the light is constantly illuminated (once a wheel has been turned after start up)?
On some other cars I've seen the light comes and goes as you are driving, but this one is on all the time.
Pretty certain the Carlton's ABS has a diagnostic line out to the diagnostics port... ...but as far as I know, only a Tech1/1a (with the Carlton Cartridge and adapter) can read it.
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Thanks, we have a Tech1 with the appropriate (Lotus) cartridge, but I don't remember seeing any ABS diagnostic options on the menus, but will check next time I have one plugged in.
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No - there is no ALDL connection to the Carlton ABS unit. I don't think the ABS ALDL connection was implemented until ABS2E systems (late Cavaliers), whereas the Carltons/Senators only had ABS2. There is/was a special test machine available to VX dealers (it's mentioned in TIS), but I've never seen one.
You basically have to unplug the ABS control unit (under the front passenger seat) and use a voltmeter to probe all the sensors on the wiring harness side. The Haynes circuit is correct for all Carltons/Senators AFAIK. Check the resistances between pins 6&4, 11&21, 8&9, and 24&26. Can't remember what they are supposed to be - a few Kilo-ohms I think. Also check all 8 pins to a chassis earth. They should all be near infinite/open circuit.
Finally, measure the AC voltage between pins 6&4, 11&21, 8&9, and 24&26 as someone spins the associated wheel (easier if the car is on a 2 post ramp). You should see a voltage generated which reduces back to zero as the wheel slows to a stop.
If it's a faulty sensor, then one (or more) will be different to the others. The other common problem is the ABS surge relay, which is located under the black plastic cover on the ABS modulator (NSF in the engine bay).
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Thanks, we have a Tech1 with the appropriate (Lotus) cartridge, but I don't remember seeing any ABS diagnostic options on the menus, but will check next time I have one plugged in.
If its a Lotus, then there are two ALDL diagnostic plugs behind the brake servo. One goes to the Engine ECU, and for that you need the Tech 1 plus the special Lotus cartridge. The other plug goes to all the legacy stuff that is standard for Carlton/Senator, and for that you need Tech 1 plus a standard 1989-1993 Vauxhall Cartridge (or mass storage cartridge).
The legacy plug on an LC only connects to the alarm. If you replace the dashboard dial clock with the Carlton trip computer, then it can also connect to that. On other Carltons/Senators it's also possible to connect to the digi-dash, auto-box, radio and other stuff depending what options are fitted - but the LC has none of that.
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Good knowledge there, Malcolm :y
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Thanks, we have a Tech1 with the appropriate (Lotus) cartridge, but I don't remember seeing any ABS diagnostic options on the menus, but will check next time I have one plugged in.
If its a Lotus, then there are two ALDL diagnostic plugs behind the brake servo. One goes to the Engine ECU, and for that you need the Tech 1 plus the special Lotus cartridge. The other plug goes to all the legacy stuff that is standard for Carlton/Senator, and for that you need Tech 1 plus a standard 1989-1993 Vauxhall Cartridge (or mass storage cartridge).
The legacy plug on an LC only connects to the alarm. If you replace the dashboard dial clock with the Carlton trip computer, then it can also connect to that. On other Carltons/Senators it's also possible to connect to the digi-dash, auto-box, radio and other stuff depending what options are fitted - but the LC has none of that.
I have OpelScanner with the ALDL adaptor cable if that helps
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Good knowledge there, Malcolm :y
Certainly is :)
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No - there is no ALDL connection to the Carlton ABS unit. I don't think the ABS ALDL connection was implemented until ABS2E systems (late Cavaliers), whereas the Carltons/Senators only had ABS2. There is/was a special test machine available to VX dealers (it's mentioned in TIS), but I've never seen one.
You basically have to unplug the ABS control unit (under the front passenger seat) and use a voltmeter to probe all the sensors on the wiring harness side. The Haynes circuit is correct for all Carltons/Senators AFAIK. Check the resistances between pins 6&4, 11&21, 8&9, and 24&26. Can't remember what they are supposed to be - a few Kilo-ohms I think. Also check all 8 pins to a chassis earth. They should all be near infinite/open circuit.
Finally, measure the AC voltage between pins 6&4, 11&21, 8&9, and 24&26 as someone spins the associated wheel (easier if the car is on a 2 post ramp). You should see a voltage generated which reduces back to zero as the wheel slows to a stop.
If it's a faulty sensor, then one (or more) will be different to the others. The other common problem is the ABS surge relay, which is located under the black plastic cover on the ABS modulator (NSF in the engine bay).
I thought the "surge relay" was the relay with diode inside in the relay box (near the strut top) in the engine bay :-\ though it's been a while :P
2 other relays live under the black plastic cover of the ABS pump itself.
It was common for the relays to have dry solder joints that need re soldering or replacing a diode
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Thanks Malcolm :)