Hi all,

After filling up my gas tank last week (premium, always) my CEL came on for the first time in 4 years of trouble-free driving and sailing through smog tests.

My first suspicion was that I had been ripped off with lower octane gas, but would that really turn on the CEL? Really? Seems ridiculous to me...

I searched online and found an OBD II Bluetooth thingamajig for less than $20 delivered. I plugged it in, hooked it to my phone and ran the Torque diagnostic app. Result came back "No Code in ECU". I tried the "Reset" feature, but it again said "No code to reset". But the CEL is on... can that be true? Or does this type of device not work with slightly older Jags?

To test the device, I hooked it to my girlfriend's 1998 SLK to see if I could "fake" a result. No need, it came back with a pending fault in the O2 sensor, so I now believe the ELM327 doojie-whatsit is working as advertised.

So... my real questions is: Is there a known problem that will turn on the CEL but not log a code? Or do I need to shell out a 1 hr fee to a shop that will spend 5 mins diagnosing (and possibly embellishing) the problem? Is it possible that my next fill-up at my trusted (expensive) local gas station might set everything right?

BTW, the car still runs as smoothly as it always has, no apparent drop in power or MPG. At least if there was, I'd have something to look for!

Anyone?

Thanks

 

Did you go to your local auto parts store? They will most likely have a scan tool they will plug in for free. Maybe a different type will show a different result. 96 is the first official year of OBDII requirement and there could be a glitch with a new (and very inexpensive) scan tool. My scanner, vintage 2007 shows the CEL off, even when it is on, but it does show the codes (0420, 0430) and does clear them and the "Check Eng." light. Funny!

 

I THINK (no absolute guarantee) that even with a '96 you should at least get a P1111 (diagnostic cycle completed) so maybe you're not talking to the OBD.
OBDII standards were introduced 'during' MY 1996 as Richard says.
Follow his advice to start with.
There are, unfortunately, codes an OBD reader can't read that will set a restricted performance flag.

 

Your problem may very well be the device you bought online.

There are lots of interfaces out there using fake ELM327 chips. You said yours cost $20 delivered. Legitimate ELM327 IC chips alone run from $19 to $28.50 with no discount for volume purchases.

Interfaces using the fake ICs have been reported as unreliable. Some programming requests and commands are not supported by the engines OBD system. As SleekJag12 said, 96 was the first official year for OBDII, and their could be a glitch somewhere which allows it to properly communicate with your girlfriends car but not yours.

I would drop by an Autozone or other such parts house and have them connect their scan tool just to see what it says. Can't do any harm, and it's free.

 

Are you using the free Torque app? I'm on my 2nd cheap Elm327 dongle and both have worked fine (for a while) with my '95. I did notice when I was first checking things out, with the free app, it returned two codes (don't recall what they were) for what was really a P0411. Even with the free app, it got the P0171/174 right that the S-types were showing. My X300 pops an air pump (P0411) on a recurring basis -every few weeks...so was surprised to get two new codes the first time the CEL popped after I bought the dongle. Hooked up the $30 OBDII reader I had before discovering Torque and it showed P0411. Bought the Torque app for $4.95 and tried again, got the P0411 with the dongle. The problem I have had is after some months of use they start to report bogus temps....eng oil at steady -40F etc. So far, even my "bad" one looks ok on code-reads and fuel trims, etc.