no check engine light, still check for codes

[whiteturboz89]

hey guys currently my engine does not have any check engine lights on but has been getting bad gas mileage and low idle even when the car is cold. Is it possible for the ecu to fail and not notify me about my problems? Basicly i wanted to check for codes but my friend said its pointless with no check engine light on.

I know this sound like a stupid question, couldnt find much in serach thread

 

[snowman]

The bulb may be burned out.

 

[hvyman]

still check for codes. Very few codes will actually stay on. Most will be stored.

 

[whiteturboz89]

If i disconnected the battery and reset the ecu. How long does it take for the ecu to start picking error codes? Been 3 days now
The check light bulbs turns on beofre i start the car so the bulb isnt broken . Thanks for the repley

 

[hvyman]

Depends on what code it is. Different trip ministers for different systems.

What are your issues.

 

[mkiii222]

If it's been 3 days I'm assuming you've started/driven it a handful of times which would definitely set codes.

Bad gas mileage can be a number of things including (but not limited to) fuel pump, injectors, o2 sensor, manifold gaskets, afm...

Check codes and report back.

 

[snowman]

With a cheap scanner its not going to report anything with no check engine light on because the ecu doesnt see anything. That's my understanding. Those 1000 dollar snap ons have the ability to open dpfe's and iac's and all that stuff. It really depends in my opinion on what kind of scanner it is. It's like either 3 starts to report or 30 minutes driven. But your mileage may vary lol. But for the record, I'd for sure say check it anyway why not lol. First plug in, then turn key. NOT turn key, then plug in, that is bad for the ecu I've heard.

 

[hvyman]

No scanner needed to check for codes. Simple paper clip will do.

 

[snowman]

is the correct way to do it to short out t1 and e1?

 

[hvyman]

Yes. Short that out and count the flashes. There's no obd2 connector.

 

[snowman]

Awesome!

http://www.cygnusx1.net/Supra/TechTips/engine_error_codes.aspx

 

[iruyle]

Yes, you can have an ECU fault without an engine light.
I had a super rough idle issue a while back and determined by pulling plug wires that only three cylinders were firing. No engine light. It began instantly while I was cruising on the freeway so I thought it had to be something simple like the ECU. I checked the codes (super monitor, FTW) and had 14 and 41, which started me errantly wasting days looking at throttle position sensors. I got fed up and just bought a used ECU anyway. Upon taking my glove box out to install it, I found that the small connector had just come unplugged. Hooked it back up and problem solved.