Main Relay Repair

[NZNick]

I changed my main relay out today using Kaz’s procedure - took me quite a while, mainly because my (DBW) car has a wiring harness in front of the two relay connectors which made it awkward to undo the connectors to get the old one out, as i have big hands. The carbon kevlar seats also don’t go forward far enough for an oaf like me to get in there. It would have been easier with the seats out, but I didn’t feel confident enough to take that extra step.
I’ll aslk a friend who is a University Electronics technician to inspect the soldering on the old relay, and reflow if necessary.
The top trim piece isn’t perfectly in place, but it’ll do for now. If it starts squeaking I’ll have another go at it!
Thanks once again to Kaz, britlude and other forum members who help us inexperienced owners out - it really is appreciated.

[Old guy]

The main EFI relay on my 2000 died and stayed dead without prior warning signs back in 2021. Fortunately, it had the good graces to do this while parked in front of our house. I had a spare in the trunk so 30 minutes of messing around with the interior trim panels and I was on my way. I did manage to snap a retainer on the top panel which required an order from Amayama.

The failure points on the relay were the heavy current carrying solder joints where the actual relays are attached to the circuit board. This is a photo showing a failed solder joint on a relay



The rectangular pin is one of the heavy current carrying pins on the relay. You can see the failure point around the periphery of the pin. The pin on the right is one of the relay coils and shows what a good solder connection looks like. The failure does not look like a simple vibration related fracture, although vibration may help it along. I expect that the damage is due to heating and migration of the solder around the pin.

This photo shows the location of the two relays on the board (circled areas) after removal of the conformal coating and partial solder removal prior to repair. The area circled in blue is the pin in the close up photo.



None of the solder joints along the left side where the sockets attach to the board showed any signs of solder fractures. That is where I expected the failure to be located. What is particularly interesting is that the failed solder connection on the relay in the close up photo is connected via the PCB trace directly to one of the pins on the socket connection. Both solder connections are carrying the same current. The surface area of the solder joint at the socket connection actually looks smaller than the relay connection; but, shows no apparent signs of damage. This suggests that the failure problem is not a design current density problem; but, perhaps the way that the relay is soldered into the board. Perhaps in the wave soldering process the large metal parts of the relay did not heat up quickly enough which resulted in a poor quality solder joint.

The repaired board is now tucked back into my spare parts box to cover for failure of the replacement relay.