ECU Fault Codes - what do they really mean?

G

geetee

Active Member
I've seen lots of contradictary information on here as to what an ECU fault code ACTUALLY means.

I don't mean what does each code mean, that is well documented.

The 2 interpretations seem to be......

1. If you get a fault code reported by the ECU, then it has detected a fault with the particular sensor or the circuit to it.
Thus the ECU takes precautionary measures. i.e. I can't get anything sensible from the DET sensor so I'm retarding the timing and jamming open the boost solenoid til you sort it out.

2. A particular sensor has been triggered. i.e. the DET sensor detects detonation.


I am favouring option 1 as I have seen info that the DET sensor will only trigger ignition retard in the ECU whilst the detonation is occuring and then the ECU reverts back to normal function once it stops.

I think this is an important thing that we need to get straight, particularly for our new members who may misinterpret previous posts regards ECU fault checks.

e.g.
Q. My car seems down on power. Is my car detonating?
A. Dunno. Do a Fault Code Check - that'll tell you.

If option 1 is correct - no it won't!

Sorry, long post :(

Someone has a definitive answer :lol:

Cheers
GeeTee 8)
 
M

MarkTurbo

Well-Known Member
Option 1 :wink:

Using the det sensor example, even when it does detect detonation and go into limp home mode it dosent come up as a fault code.

Same with all the other sensors. You only get a fault code if the sensor or the circuit for that sensor is actually faulty :wink:
 
S

skar

Guest
well from my experience i would say option 2. When i do a fault code check it always brings back DET sensor. I have yet to see any performance drop. I still havent been beat by a wrx :lol: and yea, you get the picture.

only reason i can imagine that would bring up the DET sensor, is to tell me that the car has pinged. that or my ecu is about to melt :?

kon
 
G

GINGA

Active Member
As Mark said if you are getting det there will be no fault code the ecu will just go into safe mode (-10 degree advance and boost cut to standard actuator pressure 0.5bar if you are still using the standard solenoid )and will stay in safe mode until you switch the ignition off and restart the car again if no det is then found it will be fine again :wink:
If you have a problem with the system eg bad connection, faulty sensor etc then a fault code will be logged on the ecu even if it fixes itself straight away and will stay on the system for 50 starts of the engine so you could hit a large bump in the road and cause a very brief connection fault in a circuit the ecu will log it but nothing else will happen and you'd probably never know anything had happened unless you checked the fault codes :wink:
Their is a diffence between safe mode which only happens when det is detected and limp home mode which happens when a serious problem is detected for instance a wire breaks on the maf circuit the engine can no longer tell how much air is going into the engine so should in reality not run but the ecu will go into limp home mode running of a very safe base map in the ecu that goes by revs and throttle position and will restrict the revs to about 2000rpm max so it will allow you to still drive the car and get home but will not allow you to do any real damage unless your realy stupid that is :roll: when in limp home mode the engine management light on the dash will be constantly lite to tell you this :wink: when in safe mode all you'll feel will be a lack of power and probably alittle hesitance while driving.
 
zia

zia

Active Member
also there two type of code or fault rejestering one is the normal disconnection of curcuit which normally be logged and the other type permenent type, the first type is normally reset when the car is started after 50 start the other type remain on the ecu until wiped from memory!

zia
 
S

skar

Guest
zia said:
also there two type of code or fault rejestering one is the normal disconnection of curcuit which normally be logged and the other type permenent type, the first type is normally reset when the car is started after 50 start the other type remain on the ecu until wiped from memory!

zia
Click to expand...
i clear the code yet it always comes back... only time i feel loss of power is when the ecu cuts my timing when i am in bad traffic on a hot day... does this mean my det sensor is fine?
 
A

andygtir

Member
itll stay lit until the test begins, somtimes its hard to get a connection on the pins- keep moving the parperclip or whatever you use around until it stats blinking at you.
 
M

MarkTurbo

Well-Known Member
Basil said:
Their is a diffence between safe mode which only happens when det is detected and limp home mode which happens when a serious problem is detected
Click to expand...
I meant to say safe mode not limp home mode in my first post :wink: :oops: :oops: :oops:
 
You must log in or register to reply here.
Top