Check engine light

[aaronck]

On my 2003 TJ 4.0, the light seems to come on all the time.  It's not just the gas cap, which I always take off and replace when it comes on, but everytime I wash it it'll come on, as well as various city driving will trigger it.  It seems to run a little rougher sometimes as well...is this normal?

[TaTtOo]

have you chaecked your o2 sensor... mine was doing the same thing about a month ago and that is what it was

Cheers
Lawrence

[frenchy]

Diagnostic Trouble Code(s)
Turn the ignition key to the "On" position three times in succession (i.e., On, Off, On, Off, On), within five seconds

The Malfunction Indicator (Check Engine) Lamp will flash the appropriate number of times to indicate the DTC number, with a short pause between the first and second digits  (e.g., 2 flashes of the MIL, followed by a short pause, followed by 5 more flashes, indicates error code 25)

more info here:
http://www.webejeepin.com/Check-Engine.htm

[01sahara]

Diagnostic Trouble Code(s)
Turn the ignition key to the "On" position three times in succession (i.e., On, Off, On, Off, On), within five seconds

The Malfunction Indicator (Check Engine) Lamp will flash the appropriate number of times to indicate the DTC number, with a short pause between the first and second digits  (e.g., 2 flashes of the MIL, followed by a short pause, followed by 5 more flashes, indicates error code 25)

more info here:
http://www.webejeepin.com/Check-Engine.htm

Same use of the key and a newer TJ will put the numeric code up on the odometer read out, so you do not have to count flashes. My 2001 sends the code for the evaporate control system all the time.

http://www.ptcruizer.com/computer-codes.html

[frenchy]

Nice !!

my '75 cj5 does none of the above.  

[aaronck]

Thanks guys
I got both
P0121 Throttle Position Sensor Circuit Insufficient Activity
P0123 Throttle Position (TP) Sensor Circuit High Voltage

Is it serious?

[bae146]

Thanks guys
I got both
P0121 Throttle Position Sensor Circuit Insufficient Activity
P0123 Throttle Position (TP) Sensor Circuit High Voltage

Is it serious?

I wouldn't say it is terminal.......  Check your electrical connections to your throttle position sensor and see if the contacts are dirty or loose.  TPS sensors are not the most reliable on the jeep.  I don't know what the test for the sensor would be.  Does anyone know how to test one of these with a multi meter?  Is it just a variable resistor?

[NS-jeeper]

Let me know how it turns out because my buddies 2002 TJ gave  him the same "high voltage" code when I put the code reader on it, but I didn't know what it was.

[mudpig]

with 2 tps codes i would be inclined to replace the sensor. not very expensive

[4PLAYZJ]

a TPS works on variable resistance using a 5 volt referance signal from the computer.  If the computer see a voltage above roughly 4.5 volts or belove .5 volts it will set a fault code accordingly.  The insufficiant activity usally shows that the voltage signal from the TPS is not changing as the computer would expect it to based on other sensor signals ie. map, maf or iac.  I would change the sensor first since they are relativley inexpensive.  Make sure to do a good job marking the sensor when removing it and put the new one back in the same position.  Believe it or not the small amount of play in the bolt holes can change it's position enought to slightly mess up its values.  Normally we set the TPS sensor positioning with a scan tool but since you dont have one just mark the heck out of it and you should be fine. Good luck.

[aaronck]

It went away for a while, and now it's come back twice in a couple of weeks, but it's now hesitating, almost stalling, and makes a sucking sound when accelerating.  it went away, sound and all, but now it's back again...any ideas?  I'll check and see if it's the same code 

[Matty__e]

i went threw this like 2 months ago.  check your vacume system to assure everything is connected.  i have a 03 jeep tj sahara.  It ended up being one of the vacumme lines that are connecrted to the manifold...after connected i reset codes and not a problem since

[aaronck]

It comes and goes, so I'm not sure it's a vacuum line, but I looked anyways...I think it's got to be the TPS
Is this a dealer item?  Should I install it myself or have someone do it for me?

[SmilinVamp]

Yes, replace the TPS - 99% of the time it's the sensor that is screwy.  Engine run fine forever - sensors break if you look at them the wrong way. 

 'With all things being equal , the simplest explanation/answer is normally the right one' - Hakim's Razor

[apex]

Hakim or Occam?