Symptoms of a bad thermostat can be divided into two types:Thermostat stuck open: When the thermostat is stuck open, the engine temperature drops below normal when driving, especially on the highway in cold weather. A stuck-open thermostat can also cause a lack of heat from the heating syste...
Whenever there is a suspicion that the problem might be caused by a crankshaft position sensor or if there is a related trouble code, the sensor must be visually inspected for cracks, loose or corroded connector pins or other obvious damage. The proper gap between the tip of the sensor and ...
The service bulletin for Nissan Maxima dated March 2004 mentions replacing an air/fuel sensor as a solution for the code P0171. Another Ford TSB for a number of late 90-s Ford vehicles describes a problem with MAF sensor contamination where both codes, P0171 and P0174 would appear together....
as well as surging on light acceleration. In a diesel engine, a bad EGR valve is one of the causes of a black smoke. The Check Engine light might also come on in either case.