Check Engine Light Flashing Erratically - S15 ECU

[LoSt180]

SPEC: 97 240SX with S14a SR
S15 ECU and Wiring Specialties harness.

Today I took my car in for emissions testing, in MD they connect to the OBD2 port on the car. I'm fully aware that the OBD2 port is essentially dead with my SR swap, but I needed an emissions "failure" to start the waiver process.

Before I even left, I noticed my CEL blinking rather erratically. Basically it would flicker on an off, sometimes stay on for a few seconds, then goes back out. I have a Consult cable and the Nissan DataScan app on my cell phone. The ECU has code 55 "all clear." It still has full boost (i.e. not limping at just wastegate pressure) and drives just fine. After monitoring the values for a few minutes, I can verify that the blinking CES light is related to the O2 sensor. The light comes on when the O2 sensor value drops and turns off when value goes back up.

Could an OBD2 scanner have shorted something out in the ECU? The OBD2 port has a 12V, KLINE, and 2 ground wires. I'm assuming the OBD2 "KLINE" wire just isn't connected at the F3 connector since the SR doesn't have a corresponding pin. Kinda stumped.

Everything has been running great for over a year now and the CEL only started blinking this morning after a scanner was plugged into the (pretty much useless) OBD2 port on the car.

Any thoughts?

[zombiewolf513]

Theres a CEL mode that blinks to correspond with o2 sensor operation. The FSM should have a part that explains how to change between the different modes. Most likely jumping a couple of wires at the consult/obd2 connector momentarily.

Out of curiosity, are you using an s15 valve cover, MAF, injectors and coilpacks? Or just the ecu somehow?

[LoSt180]

Thank you! The S15 FSM explanation of "Diagnostic Mode 2" is exactly what my CEL is doing!

Mode II - Engine Running
HEATED OXYGEN SENSOR 1 (FRONT) MONITOR
This function allows the fuel mixture condition (lean or rich), monitored by heated oxygen sensor 1 (front), to be read.

With ignition On, engine not running, the CEL blinks the pattern for code 55 (all good). So my ECU is definitely in 'Mode II' right now.

Now I just need to figure out how to get it out of that mode. My S14 chassis doesn't have a "CHECK" wire on the consult port, so I can't follow the normal procedure to change diag modes. When I get home I'll try jumping the CHECK pin directly at the ECU.


I have a Kouki S14 SR, to run the S15 ECU I just had to move 2 pins at the ECU connector (WG solenoid & VTC solenoid) and change out to S15 injectors. The S14a & S15 MAF is the same. Still using S14 ignition.

[LoSt180]

Figured it out. The "check" pin on the ECU was wired to the OBD2 port. I suspect wiring specialties did that on purpose so people who don't have a consult cable can put the ECU in diag mode, since the U.S. S14 KA doesn't have a "check" pin on the consult port.

Jumped the OBD 12v with the check pin for 2 seconds, no more wonky CEL.

http://i6.photobucket.com/albums/y240/lost_180/maintenance/PhotoGrid_1438907801776.jpg (http://s6.photobucket.com/user/lost_180/media/maintenance/PhotoGrid_1438907801776.jpg.html)

[zombiewolf513]

Nice, hopefully anyone with this problem uses the search tool to find this thread.

[peoperme]

The S15 FSM explanation of "Diagnostic Mode 2" is exactly what my CEL is doing!http://goo.gl/eycghd

[Hoffman5982]

I'm having the same issue but I have a 95 chassis with zenki sr, so no OBD2. What wires do I need to jump?

[LoSt180]

I'm having the same issue but I have a 95 chassis with zenki sr, so no OBD2. What wires do I need to jump?
Check your consult port, and see if you have a pin next to the 12V pin (see image). You jump those two with ignition on, engine off.

http://i283.photobucket.com/albums/kk303/alfsentra/consultcarplug.jpg

If your port does not have that pin (mine didn't) or if the consult port isn't wired up when you did your swap, then you will need to apply 12V to the ECU pin directly. Look up a Zenki pinout and look for something like CHECK or CHK CONSULT.

Probably too much info, but the consult pins on the ECU are: tx, rx, clk, & check (not to be confused with the actual check engine light pin). The consult port will have those plus 12V and ground.

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