Went to take my '03 i35 in for a smog and it passes everything except that the check engine light won't light up when you turn the key on. I took the instrument cluster out and switched bulbs with the oil light that is working and the check engine still won't work. It's like the socket is dead.

Has anybody else experienced this problem?

 

The ECU acts like a switch to light up the cel. You can start by seeing if the wire in the ECU connector for the cel is going to ground when the light is supposed to be on.

Also check to see if the printed circuit board for the instrument cluster has cracked. You have to check continuity of the 2 traces that are for the cel from the lamp socket to the wire harness connector.

 

Had a similar problem, the light did not work when turning the key to "ON", however it did work when there was an actual code in the system. In the end I soldered an extra diode running from another indicator light to the check engine light (in the instrument cluster) just to pass an emission test. Left it like this since it would still work when a code is present. Most likely, the problem is within the ECU, I looked at schematics in order to find any "feedback" wiring, but could not find anything.

 

Great advice guys. As I got to looking further into it I found the SES light it soldered to the board. The diode looks like it would do the trick. Vbtinfo, did you perhaps have a photo of your mod?

 

Here are the pics from my prototype instrument cluster. There are actually 2 diodes, the second is to prevent leaking signal back to ECU when it's not expecting it (otherwise it would trigger MIL failure code). For this you need to cut pin 45 on the M34 connector and solder 2-nd diode in between. (This info is for Maxima 2003, check if pin numbers and connector number are the same for Infiniti). The first diode (long legs in the pics) just connects pins 68 and 45 on the connector (not the cut part). Hope that helps. EDIT: Forgot to mention - changes in schematics are in red.

EDIT2: Sorry the description is incorrect, was not remembering clearly as I did this a few years ago. 1-st diode connects from pin 68 to the cut part of the pin 45 on the board, not on the connector.

 

Thank you Vtbinfo for the pic. I may end up doing that. I went the quick and dirty route and made a jumper wire from the oil LED to the SES LED. I just need it to pass smog as my reg is up. Then I can pop it back apart and do this mod correctly.

 

If you want to keep it simple just add a switch to that jumper wire and use it only when you need to pass the emissions. That way your car won't go into the fail-safe mode when an actual code would pop-up. I believe this mode is engaged when ECU detects MIL failure and there is another code present. In this case you RPM is limited to 2500.

 

Good advice, thank you

 

I've had this issue on my car a few times; it seems to come and go. I've never noticed anything performance related with regard to the SES light not coming on for bulb check. Last time time did this, I knew there was still a code (P0400, FWIW), but like I said, no drivability issues.

 

I bought an instrument cluster from an '02 i35. It didn't fix the problem so I know it's not in the cluster now. I suspect it is in the ecu.

 

Check the wire between the ECU and the instrument cluster for continuity.