Partially fried ecu

[motaratak]

I have a 1997 Sidekick Sport 5 speed. I was attempting some troubleshooting and I believe I broke the circuit that activates the "main relay". I think the tight space where the relay is located caused me to have jumpered incorrectly. With everything in normal configuration the systems that rely on the main relay do not work( no start, no fuel pump prime, etc). If i remove the relay and use a jumper wire everything appears to work correctly, i.e. engine runs, dash operates, etc. Ive tried a new relay that did not help. I think what ever component in the ecu that completes the ground and activates the main relay is inop. My ecu is the hitachi and doesnt match any of the pictures are diagrams Ive been able to find. What component controls the main relay?

[fixkick]

I have a 1997 Sidekick Sport 5 speed. I was attempting some troubleshooting and I believe I broke the circuit that activates the "main relay". I think the tight space where the relay is located caused me to have jumpered incorrectly. With everything in normal configuration the systems that rely on the main relay do not work( no start, no fuel pump prime, etc). If i remove the relay and use a jumper wire everything appears to work correctly, i.e. engine runs, dash operates, etc. Ive tried a new relay that did not help. I think what ever component in the ecu that completes the ground and activates the main relay is inop. My ecu is the hitachi and doesnt match any of the pictures are diagrams Ive been able to find. What component controls the main relay?

by hot wiring that relay you blew up the transistor that runs the main relay coil

hot working computers can get super expensive.



there is no schematics on any sport ECU (inside)
the
all I have is this.
actually there are 2 relays, main and just fuel pump.  J18 enigne's, not cars marked sport G16 are only plastic lables with that name,
J18 wide frame car is true sport.

pin C3 Pink , the transistor is blow to hell. or fuse blown #16 FI relay
or C14 main blown. same reason. or its FI fuse. (blue)

is this a J18 engine,  1.8Liters, with 2 cams? called DOHC? sold in N.Amermica's

here is the wiring.1997 and (96) in 1997 the TCM was moved to the ECU and became the PCM, that day. (does 2 jobs)

https://fixkick.com/ECU/18L/18LiterECU1.pdf


the way to blow up FP1 relay is easy, jump C3 to power or to other side of  PF1 coil boom. black/white to pink boom, or fuse blows if lucky
but the transistor is good for 0.1amps and the fuse is 15amps,  or 150 times more power than that tiny transistor can tolerate .
or pink to blue-black boom blow up ECU.(PCM) same is true for main. C14.

best is never hot wire any car with a computer ,  hard fast rule or go broke fast. (just one slip of finger and kiss off $400 for refurb PCM, or 3 times that from suzuki or more from scalpers due to rarity of car.
use a voltmeter, no need to jump pins, ever.

did you find the FI fuse yet under hood.? right fender box, j18 is here.


if curious C3 has PC traces. and if you follow them you land on a transistor blown to smithereens.
same for C14, different transistor.

the other transistor for main is C14 pin, and blows up the same way for the same reasons. fuse 7 is the only hope if not blowing that up, and 150 times more current than it can stand.
short red to blue and BOOM smoke lets out.
hoping for fuses blown, there are 3 fuses there. if you look. FI, IGcoil, and dome (memory) also they moved FI fuse to engine bay box right fender in 1996. 2 in cab, 1 in bay.

[motaratak]

Yes, this originally had the j18, it now has j23. I opened the ECU and started probing what appear to be the related transistor but it seems in good working order.

[motaratak]

I will check the fuses again and I will ensure that the relay is getting appropriate signals.    

[fixkick]

I will check the fuses again and I will ensure that the relay is getting appropriate signals.

the dead relay coil,  only has the following causes (electronics basics)
bad relay.(coil dead, contacts burned)
bad wires connectors.
bad fuse and no power to coil hot side
transistor blown. (some are just diode here that blows up or blows traces to it to hell , copper now smoke.)

the transistor is very simple and small,  and wired directly to the dead relay coil pin.

the processor turns on this transistor,as a first step. (with FP relays is way more complex ECU firmware, it must see spark or FP is kept off line, no spark , detected sets fuel to disabled)
btw the pink wire means fuel in suzuki 's !!! not main.

on other cars like used in Europe,   that same pin is the output of the alarm system , secure start up.  using wrong key , keeps the relay dead.  
I say that only due to rare possibility of having one of those non USA PCM.

good luck to you !!!!!!!

[fixkick]

these old ECU, all inputs are well protected ! series resistors and noise caps.

the outputs  do not have any protection at all, (until modern aged cars and smart outputs are born)
it is just and open collector or open drain transistor to drive all things, like relays, VSV, injectors and spark coils.
never hot wire any outputs of any computer made if savvy is the game. do not.
do not short the 5vdc wire of the ECU output to ground or to 12vdc. or boom.
we call this in electronics, letting the smoke out, with a wide grin........

some ecu's for sure 8v just have a diode there (PCB) on the main relay coil to ground to turn it on.
this is so they can add other controls on this pin for  say anti-thieft  used in other market  here.

what you find on that pin IDK, but is blown up. (fuses good)

i never did the J18 ECU ever. and are super rare cars now and even then.

I did this on g16 8v and 16v; yes
most are caused by others hotwiring good ECU. and blews up these parts easy as pie.
8v:
https://fixkick.com/ECU/transistors.html

G16b 16v main relay coil is  activated by ECU DIODE D102.  J18 IDK.

16v pins.

https://fixkick.com/ECU/16v-ecu-pins.html

sorry never did this for J18, ECU not easy to find  nor the car. nor ever any j23 seen.

but using  ohm meter with it set to buzz continuity mode finds the device that runs that pin, to main relay.

the European cars  have anti-theft box, with 1 serial comm wire to the ECU and the ECU as transistor to main relay coil
the Anti-theft box tells the ECU OK to run engine and the transistor there turns on and main closes.
this I tell you, because some cars have the wrong ECU in them.

both the FP relay and The main relay coil outputs on the ECU can be blown up easy. doing hotwiring.

Im guessing your car is USA stock but has newer j23, long block only???? we have j18  sport with J20 engines too , no mods electric..

[fixkick]

if confused and main is really fuel pump relay
the is a way more complex horse of a different color..
Fuel pumps do love to short out  and low its fuse.
here is the fender box FI is it. the last J18 ECU changed firmware such that FP relay only closes cranked or running , and not keyon. (yes that is not like G16s at all)
First is CEL lamp glows tells you main is good.


11 and 16 not blown (11 is memory DTC retention ram in ECU)