Nissan Altima Service Engine Soon Light Water Pump Problem

If the service engine soon light is on do not get a smog check. Your Nissan Altima will automatically fail the smog test. The water pump itself does not have a "trouble code". Certain failures such as high engine coolant temperature, or low coolant temperature do. Typically the trouble code your scanner will show is a P0115 (if engine coolant temperature is not normal) or P0118 (if the temperature sensor circuit has a failure).

The way the system detects trouble with engine coolant temperature is this... As your engine heats up the temperature of the coolant rises. Your Altima's engine coolant temperature sensor (ECT) is affected by the rise in temperature and signals this information to the ECM (engine control module). When coolant temperature is low (cold), the resistance within the ECT is high; and the voltage relayed to the ECM is low. As the engine gets warmer, resistance drops; and the voltage to the ECM increases. Whenever the ECM detects resistance in the ECT which does not match what it has programmed in its memory, it triggers the Service Engine Soon Light (more than likely a P0115). The ECM has a calculated table in its memory that tells it what the ECT resistance should normally be depending on how long the engine has been running.

So, long story short... you'll need to find out what exactly the problem is. Does your Nissan Altima actually have an overheating problem and requires a new water pump, perhaps a new radiator, or thermostat... or is the problem electrical, in that, no real engine temperature problem exists and the problem has to do with a fault ECT sensor, damaged/defective wiring or ECT connection, and so no. The best way to ascertain this is to dig into the trouble code itself, first. Find out which code(s) is exactly triggered and diagnose the repair from there. But either which way... if the service engine soon light is on, for any reason, your Altima will fail the smog test. The smog technician is not required to tell you this when you take your car in for the smog test, so be aware. It's not that they don't want to tell you, or they want to fail you and take your money... they are strictly required to smog test vehicles as they are driven into the smog station. This is the State's smog check requirement and a smog station can be fined for not following the procedure.