You are here:

Cadillac Repair/SERVICE NOW sensor light


My SERVICE NOW light keeps coming on. and sometimes stays on.
It cancels my cruise control when it does  this. Sometimes it goes off, sometimes not. If not, I have to detach the battery terminal for 30 secs to make it disappear.
Could it be the oxygen sensor? If so, where is it?


You are dealing with a symptom and not the cause. Service soon means you can drive it until you have the opportunity to get the emission system diagnosed and repaired. Service now is much more important and means exactly what it says. It means something is seriously wrong with the system. A good example for service now would be an alternator problem, but there are many different reasons for the service now light to come on.

The O2 sensor is located in the exhaust before the catalytic converter, but as I aid, the service now light is just a symptom of possibly a hundred different things that can be wrong and you are wasting time and money working on a guess changing possibly a perfectly good O2 sensor.
This vehicle which you did not give me the year make or model needs to have a scanner hooked to the vehicles' on board diagnostic port just below the driver's side dash to determine the exact cause of the problem. Just getting the light out is not fixing the problem. Your cruise quits because it too is part of the computer system and when that light comes on, the computer is going out of loop meaning the engine is not running properly.
I would suggest never going to a dealer and finding a repair shop that can diagnose the problem with a scanner as soon as possible. With the service engine now light on, I would not count on the reliability of the engine and it could leave you stranded some place.

Good luck!

Cadillac Repair

All Answers

Answers by Expert:

Ask Experts


Rob Painter


Alarm system questions cannot be answered on this forum. These systems are not what I can answer. Without being physically at the vehicle and not knowing what kind of electrical service has been done on the vehicle, there is no possible way to give an accurate answer over the internet. My expertise is in Ignition/key based anti-theft systems. These issues include GM VATS (resistor chip in key blade) PASSLOCK (MRD)-ignition lock rotation based, no special ignition key and the PKIII Transponder (computer chip in key) systems. These systems are not alarm based and are integral with the starting of the engine. This is why I cannot diagnose alarm problems without physically looking at the vehicle: Alarm systems are a completely different annimal than ignition key/lock based anti-theft system. Many alarm questions come from vehicles 10 years old, and since older, many hands that had been involved over the years.I am an expert in all GM factory (ignition/key based)systems. Alarm system questions pose to many situations beyond my knowledge as to what has been done to the vehicle over the years. Some guy may have actually wired the stereo into the alarm system. Who knows? Over my past 30 years in vehicle wiring repair, I have seen unbelievable wiring disaters done by guys that consider themselves "mechanics." I have seen stereos and alarms intalled using surgical tape. I have seen modules burn up, un-fused circuits, wiring jambed between the doors and even lamp cord used for a starter kill. To answer alarm questions over the internet without examining the vehicle is like asking; What does it take to remove a dent?


Education/Credentials-ASE certified. 11 years with a GM dealer and 17 years with a repair facility dealing with only the repair of theft recovered vehicles.

©2017 All rights reserved.