henshaw Posted July 27, 2015 Posted July 27, 2015 Have got ABS fault message. Have had anaysis done by garage and test says "right rear wheel sensor signal coherence" (whatever that means). As fault comes on when ignition turned on but engine not started and car not moved have thought it could be wiring/sensor fault. Have tested both sensors at (blue) plugs on top of fuel tank and circuit tester says both are open circuit as does both rear sensors on my other C5 where the ABS hasn't failed. Are these the correct connectors to check? Another (non-citroen) web says sensor test should show sensors having a resistance of 1.5kohms if working. So if the sockets have I opened to test the sensors are correct, how do the Citroen sensors work? and how do we check to see if they are faulty? Have followed Haynes manual suggestions in section 9:15. Have checked all fuses in engine fuse box, removed all plugs on fuse box and checked for cleanliness had a look at ABS hydraulic unit but coudn't see any cable sockets I could check. Have checked fuse for ABS in under-dash fuse box. Haven't taken out glove box and inspected that fuse box unit thoroughly yet. Have done BSI reset to no avail. Spoke to previous owner who said fault came on once before then disappeared automatically so thought it was a typical citroen error message that comes and goes (as they did on my other C5). What else can I do? Does one really have to lower the fuel tank to change a rear wheel sensor as the Haynes manual says? Quote
paul.h Posted July 27, 2015 Posted July 27, 2015 The RTA manual for the C5 says the fuel tank needs lowering a bit but to do this it says to undo the abs sensor connectors (via the floor hole), undo the fuel pump pipes at the same place, remove the exhaust, remove the fuel tank heat shields, put a tool under the fuel tank (use a board on a jack to spread the load and probably best to do it on a low fuel level), remove the tank bolts and then lower the tank to reach the abs wiring to unclip it (it probably does not need lowering much). Remember to use axle stands under the car so the suspension will not drop. You could also consider poking a wire and string around the tank so a new sensor could be tried by using the string to pull its connector back to the floor hole. Then see if the abs works - this would prove the fault without having to lower the tank and the clips could be fastened later. Quote
henshaw Posted July 28, 2015 Author Posted July 28, 2015 Oh Heck! Just found sensors OK. All rear sensors on my 2 C5s show the same reading. They just have a very high resistance (1.5MegOhm). Have checked cable plugs and sockets under front passenger carpet and these seem seem ok. Anyone got a good wiring diagram of what goes where into the BSI so I can do an end to end circuit line check? Would like to get a Lexia off EBay or Amazon. Which one do I need to get? Quote
paul.h Posted July 28, 2015 Posted July 28, 2015 A search on your fault 'right rear wheel sensor signal coherence' came up with the following with a few possible causes to check http://bba-reman.com/forums/PrintTopic101963.aspx Quote
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