Cooling Fans On High Cause CAN network Interference
This vehicle sets P0500 in all modules that can set it and I get heavy CAN interference whenever the fans are on high. Most noticeably when you turn the a/c on and the vehicle is moving and the fans kick on. I can disconnect the fans and the interference goes away. What I mean by interference is the CAN signals go from 0-10 volts whenever the fans are on but still produce the same waveform. It does it with either fan on or both on. I can run each fan off a separate fused power and ground supply straight from the battery and the interference does not occur. The Fan powers come straight from the engine fuse box and come out the front and go to the fans so not very much there and everything appears factory including the harness, fans and fuse box. I wouldn't think the fans would have failed and caused this because it does it with either fan and the only connection to the CAN network is the ECM supplying ground to the relays but it still does it when supplying power to the relay terminals and the relays out. Any ideas? Thanks
Did you capture a waveform of CanH and CanL with and without this “interference”? What is the resistance across H and L? Toyota doesn't show diodes in the A/C clutch and/or fan circuits any more, I wonder if the relays have diodes integrated and one failed? There should be a diagram printed on each relay.
That’s a good point, I’ve noticed sometimes bad relays I’ve replaced I have noticed on some of them, if you shake it you can hear the clipping diode broken and just rolling around inside the relay
Right off the top of my head i would suspect poor Ground. Can you perform a voltage drop on the ground side, while problem is occuring?
Hello Ryan, I am inclined think you have a ground issue. Any history of body damage or body repair? It is a good idea to start at the battery and loosen, clean and retighten, then go around the chassis and do the same with all other grounds.
Hi Ryan, It's not uncommon for electrical components to induce noise into the CAN signals. Fault tolerance is one of the main benefits of CAN. If you scope the signals with one lead across CAN-H and CAN-L, do you still see the interference? Another idea is to scope that fan motor current along with CAN and see if the noise syncs up. My initial thoughts are if there was that much abnormal…
Here is the scope capture but I actually figure it out as well! On high the fan grounds were at 5 volts. I traced it to the left front fender where they painted every fender contact point so cleaning the fender contacts and grounds repaired the ground and CAN signals.
Hello Ryan, From past experiences with shared or “piggyback” grounds, I recommend you separate the CAN harness ground away from the fan ground, so it has a clean uninterrupted ground. The reason being is as the fans wear, they will start to resonate back feed into their ground, this will scramble the CAN if it is joined.
I'll get some scope captures and check the grounds and relays once I get some time here in a little bit. I appreciate all the help guys!
The fan grounds were at 5 volts on high. They ground at the left front fender and someone painted all the contact points for the fender so I cleaned the contact areas and now we have good grounds to the fans and no more CAN interference.
… Post a resolved then . … Dan H. … Hobbs … South Texas …
Hi Ryan, Reply to your original post with your new info and then you'll be able to mark it as resolved.
That works for Questions, but the thread was started as a Discussion…
Changed it to a question and now it's resolved. Thanks!