yoda598 Posted July 24, 2023 Share Posted July 24, 2023 How common is a tcm failure? Trying to diagnose a bf fairlane ghia I recently purchased. Symptoms are : trac light comes up, scan code - steering angle circuit. Speedo drops out, shortly followed by zf sticking in whatever gear it's In. Followed by a shit ton of canbus com errors and invalid data for speed and rpm. Have Changed coils, new battery and checked alternator. Very intermittent issue. Trac light doesn't always come up and seems unrelated to zf issue. Car was well looked after before I purchased it, so I don't think it's a neglected service or anything. Will attach pic of codes. I should add that I've datalogged the individual wheel speed using forscan, they all continue to work after the issue has happened, but the actual speed output stops at whatever speed the issue happens at. Quote Link to comment Share on other sites More sharing options...
Bill Posted July 24, 2023 Share Posted July 24, 2023 5 hours ago, yoda598 said: How common is a tcm failure? Trying to diagnose a bf fairlane ghia I recently purchased. Symptoms are : trac light comes up, scan code - steering angle circuit. Speedo drops out, shortly followed by zf sticking in whatever gear it's In. Followed by a shit ton of canbus com errors and invalid data for speed and rpm. Have Changed coils, new battery and checked alternator. Very intermittent issue. Trac light doesn't always come up and seems unrelated to zf issue. Car was well looked after before I purchased it, so I don't think it's a neglected service or anything. Will attach pic of codes. I should add that I've datalogged the individual wheel speed using forscan, they all continue to work after the issue has happened, but the actual speed output stops at whatever speed the issue happens at. TCM failure happens but isn't common unless the gearbox has suffered the dreaded milkshake or it's been incorrectly handled. SAS fault C1956 is present at the time of request. Everything else appears to have cleared, so it's an issue that needs to be looked at. I'll attach an image of the ABS/DCS wiring circuit. Check power & earth circuits. Follow the CANbus circuits, noting the modules the data all passes through as there may be an issue somewhere in between. Also make sure the SAS is correctly located & not loose. I've seen one that wasn't right that caused intermittent issues. For the ABS section of the workshop manual, go to https://fordforums.com.au/wsmpub/bf/206-09.html There's very good information for diagnostic & testing, including pinpoint tests. Do these tests to rule out a SAS & ABS module fault. Speedo dropping out, gearbox not knowing what to do & having a heap of comms fault codes is very common when coils fail....even new coils. Anything that causes noise on the bus will do it. Usually, faulty coils will also cause a P0500 no speed source fault code, resulting in loss of speedo & ZF issues. If you need additional wiring diagrams, they can also be found here https://fordforums.com.au/vbportal/viewarticle.php?articleid=1818 If you need something a bit better quality, let me know. Quote Link to comment Share on other sites More sharing options...
yoda598 Posted July 24, 2023 Author Share Posted July 24, 2023 it seems the can bus runs through the steering angle sensor. so perhaps thats a faulty unit causing a communication issue. also, yaw sensor is stuck on 0. so ill replace both as a precaution. Its had 4 sets of coils, the new goss set from my territory and a set of ford coils (second hand, known working) Quote Link to comment Share on other sites More sharing options...
BeerTurbo Posted August 2, 2023 Share Posted August 2, 2023 ive had this issue on the barra r31 and more recently my turbo terry. the barra r31 was more like your setup, speedo kicks off and tcm goes into limp mode. teritory on hard acceleration would just lose speeo and trans would work fine. both were fixed with new plugs and genuine coils from ford. new and faulty coils test same resistance so came to conclusion coils can be tested for this fault, just bin them and new ones. I also tried to fix the r31 with a set of known good coils, but it did not resolve the issue. It wanted me to spend that money at ford. Quote Link to comment Share on other sites More sharing options...
yoda598 Posted August 2, 2023 Author Share Posted August 2, 2023 Funny you should mention this, I fitted new genuine coils today with a set of bkr7e (it'll se boost very soon) to no avail. I did datalog the issue and noticed even though the speedo drops out the obd2 vehicle speed is stuck at whatever speed the issue occurred. I'll post the data log tomorrow. Quote Link to comment Share on other sites More sharing options...
yoda598 Posted August 2, 2023 Author Share Posted August 2, 2023 you can see in attached datalog, the speed is working fine. however failry early on the speed freezes. ive also checked on forscan, all 4 individual wheel speed sensors continue to work. Currently thinking tcm failure or abs module failure. i have changed ; PCM, genuine ford coils, spark plugs. Ive checked all engine bay plugs and cleaned them, i have a spare tcm, not sure if i have an abs module. i have the turbo territory here im stripping but not sure the units are compatible. fairlane speedo dropping out.teclog Quote Link to comment Share on other sites More sharing options...
Bill Posted August 3, 2023 Share Posted August 3, 2023 5 hours ago, yoda598 said: you can see in attached datalog, the speed is working fine. however failry early on the speed freezes. ive also checked on forscan, all 4 individual wheel speed sensors continue to work. Currently thinking tcm failure or abs module failure. i have changed ; PCM, genuine ford coils, spark plugs. Ive checked all engine bay plugs and cleaned them, i have a spare tcm, not sure if i have an abs module. i have the turbo territory here im stripping but not sure the units are compatible. fairlane speedo dropping out.teclog 841.89 kB · 1 download Is the noise suppressor under the intake manifold connected & wiring ok, good earth? Not sure if it also reduces noise on the bus, but it's connected directly to coil wiring & back to the PCM via the A connector & meant to suppress radio noise. A faulty PSP switch & wiring will at times cause very weird issues but not cause a fault code. Have you checked if there's a consistent pattern ie when trans TOT reaches a set temp, rpm & load? Quote Link to comment Share on other sites More sharing options...
yoda598 Posted August 3, 2023 Author Share Posted August 3, 2023 1 minute ago, Bill said: Is the noise suppressor under the intake manifold connected & wiring ok, good earth? Not sure if it also reduces noise on the bus, but it's connected directly to coil wiring & back to the PCM via the A connector & meant to suppress radio noise. A faulty PSP switch & wiring will at times cause very weird issues but not cause a fault code. Have you checked if there's a consistent pattern ie when trans TOT reaches a set temp, rpm & load? I actually haven't looked to see if it's there. Psp as in power steering pressure switch? Interesting.. never heard of them causing an issue.. No pattern that I've noticed. It's by far the most unpredictable issue I have had to date. Quote Link to comment Share on other sites More sharing options...
Bill Posted August 3, 2023 Share Posted August 3, 2023 (edited) 16 minutes ago, yoda598 said: I actually haven't looked to see if it's there. Psp as in power steering pressure switch? Interesting.. never heard of them causing an issue.. No pattern that I've noticed. It's by far the most unpredictable issue I have had to date. Yes, power steering pressure switch. Usually due to it causing VREF or SIGRTN to open circuit or ground. I've had one where spinning the top section of the switch & flipping the wiring over itself whilst doing this would influence the fault. Edited August 3, 2023 by Bill Quote Link to comment Share on other sites More sharing options...
yoda598 Posted August 3, 2023 Author Share Posted August 3, 2023 Yeah right. I'll have a look. Being that the steering angle sensor also freezes up with the speed. I'm leaning towards the abs unit. Quote Link to comment Share on other sites More sharing options...
yoda598 Posted August 9, 2023 Author Share Posted August 9, 2023 On 8/3/2023 at 1:16 PM, Bill said: Yes, power steering pressure switch. Usually due to it causing VREF or SIGRTN to open circuit or ground. I've had one where spinning the top section of the switch & flipping the wiring over itself whilst doing this would influence the fault. Have had it unplugged, same issue. Also unplugged noise suppressor same issue. Fitted a replacement abs module today, same issue. Last thing to swap is tcm. Quote Link to comment Share on other sites More sharing options...
Bill Posted August 9, 2023 Share Posted August 9, 2023 8 minutes ago, yoda598 said: Have had it unplugged, same issue. Also unplugged noise suppressor same issue. Fitted a replacement abs module today, same issue. Last thing to swap is tcm. Unplugging the noise suppressor will stop it from doing its intended job. Noise suppression. I haven’t seen a faulty TCM that hasn’t produced fault codes but yours could be the first. Let us know how it goes. Quote Link to comment Share on other sites More sharing options...
yoda598 Posted September 7, 2023 Author Share Posted September 7, 2023 Extremely late reply but I wanted to be sure the issue was resolved as I've been tricked before 😅 It was intact a faulty powersteering switch. Disconnected it and 75+ hours with 0 issues. Turns out that when I had it unplugged before the abs module wasn't the original as I was chasing the issue ect. So went back to abs module from the fairlane and all sorted! Quote Link to comment Share on other sites More sharing options...
Bill Posted September 7, 2023 Share Posted September 7, 2023 10 hours ago, yoda598 said: Extremely late reply but I wanted to be sure the issue was resolved as I've been tricked before 😅 It was intact a faulty powersteering switch. Disconnected it and 75+ hours with 0 issues. Turns out that when I had it unplugged before the abs module wasn't the original as I was chasing the issue ect. So went back to abs module from the fairlane and all sorted! Thanks for the update. The PSPS & wiring are often overlooked but are known to cause weird issues. Quote Link to comment Share on other sites More sharing options...
yoda598 Posted December 24, 2023 Author Share Posted December 24, 2023 I was wrong! See attached images! Quote Link to comment Share on other sites More sharing options...
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