AnsweredAssumed Answered

Repeat LIN failure with TJA1020

Question asked by Mike Adema on Mar 6, 2020
Latest reply on Mar 9, 2020 by G.w. Sun

Hello. I'm just a mechanic trying to fix a problem car, but here's the story.

 

I have a vehicle that has had a repeat failure of the LIN bus. This has required the cluster to be replaced each time to get LIN communication active. In less than a year, it has gone through 4 clusters and now they're discontinued. Each time I get the vehicle back, the LIN is "stuck" at about 1V. With every cluster, scoping the LIN circuit out of the cluster did not show any voltage spikes that may harm the circuit while manipulating everything controlled on the LIN bus. In our world, all trouble shooting would point towards replacing the cluster, but I know that won't last. I am looking for any insight as to what might take the LIN bus down. I have connected an IC test clip directly to the chip and checked all eight legs for something abnormal. The chip on this board is a TJA1020. The Vsup and NWake signals mirror each other with key on and start up and follow battery voltage. GND stays at 0V. TXD has a 5V pull up pattern, repeating (about 2 sec) with a break. Just before the break in TXD, both RXD and EN will signal at the same time like a synchronizer signal. RXD is a 5V pull up and EN is a 5V pull down.

 

Other than a voltage over spike, what could stop the chip from producing a signal on the LIN circuit? Does the NWake circuit need a signal (like a ground pulse) to get the chip operating? Would a low voltage on Vsup (like a bad battery during engine cranking) cause a failure?

 

Thanks for any input.

Mike

Outcomes