SQ6 Driving Relays

[Robbied]

Hi,

I’m in need of some urgent advice/info on an issue I have with a new harness/ecu at the moment! Hope someone can shed some more light on this!

SQ6 driving a Pi Omega (d1) in ‘dumb’ mode. Pretty basic chassis harness as the car doesn’t have to be street legal.
We are using the ECU to drive relays controlling Fuel Pump, Radiator/Intercooler fans and a water pump (using low side PWM’s, 3,5,6,17,18) and here seems to be our problem.

With the relays disconnected, the ECU will shut down correctly from the IGN switch (and pin 49, IGN 12v, goes to 0v). As soon as you connect any of the relays, we think the ECU sees some residual voltage through the relay coils and won’t shut down properly. When this happens, it pulls the ECU 12v pin (49) to around 6-8v and not 0v. This isn’t good....!

I have tried adding diodes (1N4001’s) in line in the PWM outputs, this is stopping the ECU seeing 12v from the relay (relay pin 86, and effectively allows the ECU to shut down) but also means you can’t pull the relay to GND and operate the output!!! So it’s no good. If the diode is fitted the other way around, I have my original problem still.....

This is driving us mad as we can’t find a solution and hence, can’t really run the car properly, although, all other functions work properly and the engine will fire up no problem.

Can I use the PWM’s ‘inverted’ and then ground the relays so that the ECU adds the 12v and operates the relay coil? Or is there not enough duty cycle on the high side PWMs to hold a relay contact open or closed?

I’m surely not the only person finding this problem, but although the ECU seems to be functioning correctly, is it possible I have an internal fault in the SQ6? Of course, i’d like to rule out any wiring issues before trying another ECU or sending mine to Pectel for a bench test.

Thanks for any help...!

-Robbie

[Neel]

Is this a system and harness Apex sold you? I'd like to see the harness design.

[Robbied]

No, im based in the UK, its not an Apex system,

But I am struggling to get this sorted and as ive been browsing the forum on and off for a while, I though it was worth posting...!

The ECU seems happy to do everything correctly until I introduce a relay to a PWM output,

[Neel]

No problem, we help everyone here! I was just hoping we had a wiring diagram. So you know, we had relay issues with some ealier software (1.21 maybe) so you might want to contact your dealer for an upgrade. Otherwise, give us more details about how its all wired....

[Robbied]

Ok so heres some info on how its all linked up....!

ECU PWM 3 (pin 33) splits and goes directly to pin 85 of two N/O 40A relays. These relays each switch on an Bosch 044 pump (via Pin 87). Pins 86 on this is IGN 12v and 30 is a fused supply. System works correctly, ECU primes pumps when required and swiches off when engine stops.

ECU PWM 5 (pin 4) and PWM 6 (pin 31) are wired to two respective 70A relays (pin 85). These have a very heavy feed and fire (rear mounted) radiator fans when needed. Other relay connections are as per f/pump system.... Again system works and ECU fires fans sequentially. I also have an override on PWM 5, just a toggle switch that takes the relay coil GND direclty to GND overrides the ECU if needed.

PWM 17 (Pin 30) again works exactly as the fuel pump system. But this time the PWM grounds a smaller 20A relay and this switches on an electric (rear mounted) water pump. Once again, system works at desired temp and i can have the water pump run-on etc etc.

So, all these systems appear to work but with any of the above relays in the system, the ECU wont shut down when 12v is removed from the Vbatt pin (49). If i hard wire the pumps to run the car, everything is fine and ECU appears to behave correctly....

I've never had this kind of problem before, and have used an SQ6 in this way on a different vehicle with out issue.

Thanks again for any help!

[Neel]

Are you sure that power is actually removed from pin 49? Its often the case that relays will backfeed the system if the main ECU power is also tied in with some of the relay power.

[Robbied]

Im pretty certain that the ECU 12v is on its own switch and that when I power up the loom without the ECU connected, and open that switch, I lose my +12v as expected.

Although the IGN 12v for the ECU is also the IGN 12v for the alternator, I believe i still have my problem even with the alternator (standard Mitsubishi 120A item) disconnected....

[Neel]

I've never seen this in the 100+ SQ-6's we've done. Can you build an adapter or backprobe the pin to verify that 12V really does go away? I've seen many, many cars that backfeed the 12V main power through unexpected sources.

[Robbied]

Thanks, I will try this and see what happens.

[Robbied]

We finally got somewhere with this. It seems the relay coils were staying live when the ECU was shut down, therefore allowing the SQ6 to see 12v on its PWM input pins (as it does when its powered up)

Ive since discovered the T6-2000 doesnt like this either, and we've modified the looms to suit.

[Neel]

This is a common error and exists with many aftermarket ECUs. Its very important that the power side of all relays AND the power input on any aftermarket ECU are from the same source.

-Neel