First read the diagnostic fault codes to rule out any obvious problems. You can do that yourself by cycling the ignition switch from "off" to "run" three times within five seconds. Leave it in "run", then watch the code numbers appear in the odometer display.
It takes a specific set of conditions for a fault code to set to indicate a sensor circuit is causing a problem. Before that occurs, it is also possible for a sensor to develop the wrong signal voltage but one that is still within the acceptable range. If it stays in that acceptable range, no fault code will be set to direct you to the circuit that needs to be diagnosed. For that, you have to use a scanner to view live data and determine if any reading looks suspicious.
Besides sensor readings, the scanner also shows fuel trim numbers. If you see high positive numbers, it means the engine computer is adding fuel to the pre-programmed starting point. It thinks more fuel is needed in response to something, and we have to figure out what that is. If the numbers are high negative, it means the computer wants less fuel than normal, and we have to figure out why too much fuel is going into the engine.
Those are problems for an engine performance specialist. The clue is there is usually some related fault code set to get him started. When there are no codes and no running problems, the next suspect is a sticking brake. The first observation is one wheel will be unusually hot after a short drive. Another potential clue is the brake pedal is higher and harder than normal when pressed. If you stop on a slight incline, shift to "neutral", and release the brakes, the vehicle should creep downhill on its own. If it does not, we need to determine if brake fluid is being trapped and is unable to release from one brake, or if a mechanical problem with that brake is the cause.
Monday, April 2nd, 2018 AT 12:10 PM