I'm new here looking for some help; I've looked through other similar posts with no luck. I have a 95 d21 2.4l with only code 12 no CEL. Running very rich and I cant rev past around 2000 rpm (Guessing cause RPM gauge is not working) I replaced the MAF connector and checked power - 12v, checked ground - 12v, and I have continuity and no resistance between the sensor connector and pin 17 on my ECU (ECU has also been replaced with matching numbers refurbished). I've tried several different MAF sensors. 1 when I bought the vehicle, 2 from AutoZone, 1 from eBay, 1 from amazon, and now a Genuine Hitachi replacement. I've disconnected the battery to clear the code but it keeps coming back. (Key on, vehicle not running code 55; start the vehicle code 12.) I added an engine ground wire at the MAF connector because before I was only getting ~6v. The intake gasket was also just replaced before I purchased the vehicle. I've used electrical connector cleaner on the ECU connector even though there was no corrosion or debris. I've gone through the FSM but it hasn't been much help to me. Any suggestions or feedback is much appreciated. Thank you.

The FSM for this is a bit anemic with respect to an actual diagnostic procedure for this code 12 MAF issue. Adding that engine ground wire at the MAF connector is concerning and may actually be masking the electrical issue you apparently have. The schematic shown in the FSM, page EC-63, shows an ECCS relay in the circuit. https://www.nicoclub.com/service-manual ... 5%2FEC.pdf Perhaps that is malfunctioning or you have a short to ground causing a voltage drop to ~6V if in fact it should be ~12V. Adding the ground wire so that you get the ~12V reading you expect does not correct the cause of the voltage drop. Hopefully, it's just an easy relay replacement fix. Short circuits make my head short circuit if they are not obvious and easy to locate.

mdmellott wrote: ↑

Sun Aug 08, 2021 5:23 pm

The FSM for this is a bit anemic with respect to an actual diagnostic procedure for this code 12 MAF issue. Adding that engine ground wire at the MAF connector is concerning and may actually be masking the electrical issue you apparently have. The schematic shown in the FSM, page EC-63, shows an ECCS relay in the circuit. https://www.nicoclub.com/service-manual ... 5%2FEC.pdf Perhaps that is malfunctioning or you have a short to ground causing a voltage drop to ~6V if in fact it should be ~12V. Adding the ground wire so that you get the ~12V reading you expect does not correct the cause of the voltage drop. Hopefully, it's just an easy relay replacement fix. Short circuits make my head short circuit if they are not obvious and easy to locate.

If the ECCS relay was causing the problem then the whole ECM supply would be at 6V. The problem is probably in the MAF power wire and not the ground. All the MAF wires are vulnerable on most Nissans because the bundle makes a big, unsupported loop to reach the sensor and then gets messed with every time the airbox is opened. To see if it's the power wire, backprobe the power pin on the sensor and jump it to 12V straight from the battery. If the code clears then the wire is bad. You should also use contact cleaner on the MAF connector pins, they're more exposed than the ECM connections and more apt to cause issues.

mdmellott wrote: ↑

Sun Aug 08, 2021 5:23 pm

The FSM for this is a bit anemic with respect to an actual diagnostic procedure for this code 12 MAF issue. Adding that engine ground wire at the MAF connector is concerning and may actually be masking the electrical issue you apparently have. The schematic shown in the FSM, page EC-63, shows an ECCS relay in the circuit. https://www.nicoclub.com/service-manual ... 5%2FEC.pdf Perhaps that is malfunctioning or you have a short to ground causing a voltage drop to ~6V if in fact it should be ~12V. Adding the ground wire so that you get the ~12V reading you expect does not correct the cause of the voltage drop. Hopefully, it's just an easy relay replacement fix. Short circuits make my head short circuit if they are not obvious and easy to locate.

Update: Got it working. I removed the engine ground I added. I popped open the eccs relay, very minor corrosion starting, sprayed some electrical cleaner on the pins and in the connector. started it up and revs over 2000 now, still running a bit rich but much healthier. Thank you so much! I would've hated tracking down a short. Thanks to mdmellott for the suggestion as well. much appreciated.

NextGenNow wrote: ↑

Mon Aug 09, 2021 5:05 pm

I popped open the eccs relay, very minor corrosion starting, sprayed some electrical cleaner on the pins and in the connector. started it up and revs over 2000 now, still running a bit rich but much healthier. Thank you so much! I would've hated tracking down a short. Thanks to mdmellott for the suggestion as well. much appreciated.

Wow, you're lucky it was running at all with 6V to the ECU. They're usually dead horses when those relays get high resistance. The Pathy ECM relays were recalled for that, below 9V through the relay secondary and the vehicles won't even start. I'd definitely getcha a new relay if it rolled into our shop.

NextGenNow wrote: ↑

Mon Aug 09, 2021 5:05 pm

Update: Got it working. ...

Excellent! Sometimes better lucky than good.

mdmellott wrote: ↑

Mon Aug 09, 2021 6:51 pm

Excellent! Sometimes better lucky than good.

Can I hear a big amen to that?!