SXGT

I'd like to get a Master List going of all the issues you can have that WILL NOT trigger a CEL. all posts welcome.

BraMas

Just Google OBD 2 codes and your list is complete

SXGT

http://www.mikefordmustang.com/obd-II-2-codes.php


its a rather large list, would be nice to have a list to look at if you knew something was wrong but had no CEL come on.

Seabee1993

Try a chiltons manual....

BraMas

I have to ask and I don't mean to be a d!ck but do you have 2 people using the same logon in your house? One day you make a post that seems like you know what you are doing and than the next day it is WTF is this guy retarded. I mean that in the nicest way

SXGT

I've been posting on here for 8 years. I can answer most people's questions I guess. You're not the first person to bring this up to me. I think Sometimes I am bad at wording my own questions or expressing myself.



I was looking to make a list of NON-CEL issues. I dont know what common issues people have that don't trigger a CEL and making a list of NON-CEL issues with only a LARGE list of CEL codes seems tedious.

cliffyk

I'll have a stab at it (looking solely at engine control):

• Old/dying O2 sensors will cause the engine to run rich because their output voltage drops as they age--from the normal 0.2 to 0.8V to as low 0.05 to 0.6V. The PCM sees this as a lean mix and adds fuel via the short term full trims. Until the STFTs hit +25% there will be no DTC;
  
  
• The MAF (Mass Air Flow) sensor is monitored only to ensure that the output voltage is between 0.24 and 4.79V. As long as the output voltage is not intermittent, and reasonably in line with calculated load, it can be anywhere in that range, be "wrong" (as in not representing the actual airflow) and not throw a DTC;
  
  
• Both the IAT and ECT (Intake Air and Engine Coolant) temperature sensors are similarly monitored (the range is 0.2 to 4.6V); again the voltage may be within that range and be "wrong" without throwing a DTC;
  
  
• The TPS (Throttle Position) sensor is also monitored by comparing its output voltage and calculated engine load. As long as its output meets those criteria it may be "wrong" and not throw a DTC;
  
  
• The FRP (Fuel Rail Pressure) sensor is another input monitored only to ensure its output is within a given range, in this case 0.3 to 4.8V. Again this may be "wrong" in not accurately reporting the actual fuel pressure, however it the signal is within the limits no DTC will be thrown;
  
  
• Misfires occurring over fewer then 200 revolutions will not throw a DTC;
  
  
• A weak (but not completely dead) COP will generally not trigger a DTC;;
  
  
• EGR monitoring will not detect sluggish EGR valve operation, and sometimes not detect a valve that is stuck open "just a little bit";
  
  
• The DPF (Differential Pressure Feedback) EGR sensor is monitored only to ensure its output is within 0.2 to 4.5V;

I am certain there are many others, those are the ones I have run into over the years...

Dooney

IAC can also go out and not throw a CEL depending on which way it goes. I do not remember if it is stuck open or stuck shut but I had the issue of mine going out and it did not throw a code

wifes pony

now that was interesting cliffy. took my car to the shop for code readings, my man said there was not a one to be found. well my car has a terrible clicking, sounds like a bad exhaust leak. but only during acceleration. as gears change and you ease off the pedal, the sputtering and clicking seem to decrease. mash the gas, and the awfullest clicking occurs. sounds like a bad ehaust leak. exhaust is new. underhood, it sounds almost as if the sound is coming from the back of the intake, i'm thinking cracked intake manifold, cause once you've eased off manifold vacum pressure, the noise almost quits. im just guessing. dont believe a leaky exhaust, would cause the car to bog, during acceleration any help? please and thank you