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Discussion Starter #1
Our Altima will not start!
When I bought the vehicle, after a bit of pressing on the gas, the car started right up. I figured it was just water in the tank. The same day though, once I turned off the car, it would not start up right away. It would take a good 15+ minutes of pressing on the gas to get it to fire up. Once this issue started happening, the Check Engine Light came on and I was able to get it soft scanned and it came back with a Misfire in Cylinder 1 and also a Camshaft Sensor/Crankshaft Sensor error. Once I fixed those, the check engine light disappeared and the car fired right up but is now in Limp Mode. Give or take a day or two and the car once again stopped firing up at all. After an hour of pressing on the gas and trying to get it running, it just does not start. I started listening for the fuel pump and realized that it wasn't priming 90% of the time so we decided to give that a try and replace it. Tonight we replaced it and it still is giving us the same issues above. IT DOES NOT START. I'm seeking any advice possible because it's coming to a point where I have no idea what it could be and I'm very lost on the situation. Any and all advice is appreciated, thank you!

Things we've replaced: Crankshaft Sensor, Coil Pack, Fuel Pump, All new Spark Plugs and the PCV Valve.
 

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Sup Mod keeping the peace
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Before we can help you, we need to know if your Altima has a 4 cyl or 6 cyl engine. We also need to know what the actual ECU fault codes are; example: Pxxxx, where the X's are a numeric code.

The no start condition is most likely caused by one of the sensors being bad. When replacing the sensors, it's always best to replace both the camshaft position sensor(s) and the crankshaft position sensor. Always replace the sensors with new OEM components from a Nissan dealer; aftermarket sensors are unreliable, don't last long and many times are DOA.

The QR25DE engine uses two sensors. The VQ35DE engine uses three sensors.

A Limp Mode condition can be set by several different causes; that's why we need to know what the actual ECU codes are. Most of the time it's caused by a disturbance of the wiring from the MAF or the Electric throttle control actuator on the throttle body.
 

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Discussion Starter #3 (Edited)
Here are the two codes that were last seen on the Altima. It is a 4 cylinder. I'll read through all that you mentioned and respond accordingly, thank you!

Error codes: P0335, PO725

We can't start the car to see if the check engine light is on but those were the two previous codes before the light went off after we fixed the crankshaft sensor. I don't believe there the check engine light is on anymore. It cranks but doesn't start. After changing the crank sensor, it started right up 3-4 times just fine and now it doesn't start at all. No check engine codes we are aware of. We've taken care of all previous codes.
 

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Sup Mod keeping the peace
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When replacing electronic components such as sensors, always disconnect the battery first, otherwise damage can occur to the component or other components from possible electrical surges. After a repair is completed, first clear the ECU codes, then start the engine.

You can check for ECU codes without starting the engine; just turn the ignition switch to the run position without trying to start the engine. The P0335 code is a failed crankshaft position sensor (CKP). However since you just replaced it, inspect the harness connector at the sensor and make sure there are no bent pins in the sensor. If the visual inspection shows OK, then the CKP most likely is defective. Always replace the sensors with new OEM components from a Nissan dealer; aftermarket sensors are unreliable, don't last long and many times are DOA. So if it's an aftermarket item, then that may be your problem.

The P0725 code is caused by a Failed engine speed input sensor which will put the system into Limp Mode. First fix the P0335 fault, then maybe the P0725 may go away; if not, then the speed input sensor needs to be inspected. There may be a leaking O-ring causing contamination of the harness connector; if that's OK, then the sensor most likely is defective.
 
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