99 maxima SE 5 speed, service engine soon light, but no codes??

[slfalco]

Just changed fuel filter, after restarting car, get service engine soon light... Hooked up a generic scan tool, it says there are no codes... I reset it, restarted car, light was off. Next day the same thing (light pops on when starting car, no codes read out)... I checked all the wiring, connections, etc in the area I was working, I can't see anything wrong...

1) I have been shutting the car off to attach the scan tool, then turning on ignition to scan the codes.. should I maybe reset the light, start the car to get the light again, then hook up the scan tool right away (without turning off the car)? I can't understand why no code is found...

2) could there be codes stored that my scan tool can not see? I know Nissan has some tool called Consult, but I thought that a generic scan tool should be able to pick up any codes....

[loystock]

There must be a DTC code associated with the SES. Take the car to Autozone or the likes for a free scan. And make sure you get a printout of the fault codes.

[slfalco]

Yes, I took it to Autozone, and they scanned out P0135 and P0155, which point to upstream O2 sensors on both banks... Seems unlikely that both sensors failed at the same time, and since I just changed the fuel filter (had not been done in 90K miles, my bad), I will wait a while to see if the codes clear up after the ECM relearns things.. I assume the fuel pressure/mixture conditions are better now with the new filter.... Not sure why my scanner was not picking up these codes, they are generic and not Mfg'er specific...

[loystock]

If the O2 sensor fault codes persisted, then you have to replace them as soon as you can. The bad O2 sensor may cause your engine to run rich which may eventually damage the catalytic converter (OEM part is very expensive).

As for your scanner, it may not be compatible with the Infiniti OBD II protocol and pin connections.

Ford uses J1850 PWM protocol with pins 2-4-5-10 & 16. GM uses J1850 VPW protocol with pins 2-4-5 & 16 but not 10. Most Asian and European cars use ISO 9141-2 protocol with pins 4-5-7-15 & 16. Some foreign manufacturers started using CAN protocol (ISO 15765/SAE J2480, pins 4-5-6-14 & 16) in 2003. The CAN protocol is standard for cars in model year 2008 and beyond

[slfalco]

Well, I have found the problem. Due to a mixup when removing and reinstalling the fuel pump fuse (to relieve pressure to change the filter), I mistakenly ended up removing the fuse in position 31, which is the heater circuit for the front O2 sensors. I reinstalled that fuse and cleared codes, but the car stumbled during warmup, and generated codes pointing to 'high voltage' for the same front O2 sensors (it did this twice). I wonder if running the car with the heaters disabled has damaged the sensors? I am going to replace both, they are original to the car with 150K miles on them...