Wiring for power source of ecu on pathfinder 1999

code p300 refers to random/multiple misfires--misfire detected==causes--spark plugs--HT leads --injectors--ignition coils--low compression--wiring
If you are only now experiencing the problem after changing the ECU, I would suspect that wiring and connections to the new ECU may not have been fitted properly. There may be problems in the ECU CPU (chip) and it may be necessary to use a scanner to reset the CPU program to recognize the sensors of the vehicle correctly

Sorry but you can't rely on fault codes or fault code readers.

If you have a problem it is best practice to initially forget the electronics and begin with the basics - visual and physical checks as if there was no electronics. Verify the presence of fuel and good delivery and the presence of a good spark, etc. etc.

Your car may be old but it is young enough to be fitted with an immobiliser. Immobilisers can be unreliable...

If you get a fault code it is a clue and nothing more. Don't spend money until the sensor, distributor or whatever has been checked and found to be faulty using meters, scanners, live data, oscilloscope...

When you get a fault code, erase it and try again. If at any time test results are inconsistent then remember when a code says a sensor is faulty it often means the sensor and/or the circuit, which could mean wiring, connectors or even the ECU. An ECU is quite capable of telling lies, they aren't bullet-proof and can sustain damage in all sorts of ways but continue to work satisfactorily for a further year or more and then suddenly for no apparent reason begin causing trouble.

No way should you need to replace every sensor or need 3 distributors. It is hard, tedious work checking an entire management system circuit for continuity and the cleanliness of every single connection but if the results of testing are inconsistent the ECU must be suspected and due to the expense, the groundwork must be done before replacement can be justified.

follow the positive battery wire under the hood it leads to the starter

Should be under the exhaust manifold where the engine and transmission connect.

need a diagram of wires. can buy manual of go to local auto zone and they may be able to print you out one at no cost...good luck

NEED HELP....I have a 2006 Nissan pathfinder is getting over heat, already do the flash and change thermostat.. you can run it everything is ok but if you go to a far place it get over heat, I lead cold down and I can use it but then happen the same.. so I need your help please

run scanner

By using a prob/test light(make sure that battery is fully charged) If not sure if battery is fully charged try boosting with jumper cables. Then try cranking if not sound like a clicking is heard check power wire at the starter check the fthick one thats bolted on to starter for constant power (should have power all the time as long as battery is connected) then with ignition on and in cranking postion(attenpt to crank)check second wire for power there should be power when key is in crank position and will go out when key is released. IF YOU GET POWER WHEN IN CRANK POSITION .. then the starter is BAD. Replace and that will fix you atrating problem. If ther is NO power from constant power wire then it coul mean a loose positive batter pole or corrosion on terminals or may be a bad fusible link, these links are on the positive battery poll. check and make sure NONE of them are burnt out/broken. This problem could also mean a bad ignition switch too or blown ignition fuse please check all fuse. Good luck and thanks for using FIX YA, conatct if you need more help.

what is the problem with the truck?? let me know.