Questions and Answers

Nissan Pathfinder XE DTC 51 Q. Sometimes when I start my 1994 Nissan Pathfinder XE 136,000 miles, it starts off rough. Not every time, but lately very frequently with Check Engine Light. Then it smooths out and the indicator goes out. Sometimes it doesn't and continues to run rough. The diagnostic code is 51 that points to injector circuit being open.

I suspected a injector, but now I am having doubt about that. I have checked the continuity, 2.7 to 13.5 ohm, and voltage across all injectors and they read good. I checked the wire and they all have continuity. I have replaced all spark plugs, wires, cap and rotor. Could it be the ECU? Or could this be something else? I am clueless. Any help will be greatly appreciated!!!

• 1994 Nissan Pathfinder
• VG30E
• 5 Speed
• 136,000
• Fuel Injected
• ABS Brakes
• P/S-A/C-Cruise Control
• Rack & Pinion Steering

Thanks,
Frederick

A. The problem you're having is when you go to test the injectors, the are working correctly and will, naturally, check out as good.

If it happens fairly frequently, what you can do is get a noid light. You can get them at any auto parts store. The first night leave it plugged into the #1 injector connector. The next morning when you go to start it, watch the noid light. If it flashes while you start it and continues to flash when it's running, that injector circuit is good.

Of course this is only valid if it displays the symptoms with the Check Engine Light on. Then keep trying it with all the injectors down the line until you find the one injector circuit that's bad. If the light remains steady, then you have a problem with the wiring between the injector and the PCM, or the PCM is bad.

If the light fails to come on, then you have a wiring problem between the injector and the ignition switch.