'97 Explorer -- "no link" to OBD port, flunked emissions

[Austin Healey]

My wife took my truck for an emissions test today and it failed -- the DEQ report said the OBD indicator lamp failed.

I put a scanner on it, and it tried to scan the system, then returned "link error." I last used the scanner a few months ago to check for codes, and connected without a problem.

The tester at the gas station told my wife he could prolly fix the problem for $200. Since I'm my own mechanic, hopefully I can do it for less. But what's the "fixable" problem likely to be?

Also, when I turn on the ignition, I don't notice a "check engine" light illuminating. Could it be as simple as a burned-out light bulb?

Thanks for any help.

 

[koda2000]

Check your fuses. There's a fuse that provides power to the PCM/ODBII diagnostic port. #17 or #13 maybe? I don't recall. I think the cigar lighter is on the same circuit.

 

[J_C]

This seems very suspicious to me, that you suddenly get this error right after they tested it. You could just have a bulb out, or it could have been damaged before the test got that far. Bulb out shouldn't keep your scan tool from connecting, yet the bulb should be coming on when you turn the key.

I assume the tester also does repairs based on what you wrote? I am wondering if this is a deliberate damage caused scam to make profit.

I would test your scanner on another vehicle just to be sure it didn't fail. The fuse shouldn't blow just from doing a test, and the tester didn't (by your statement) claim they couldn't connect at all. This is part of the fishiness.

I too would test the fuse or wonder if the tester (person) completely removed it to perpetuate a scam, figuring he'd get paid $200 to sneakily put the fuse back in.

I could be wrong (am in general very paranoid about letting people touch my vehicles then finding "problems" that weren't exhibiting any symptoms beforehand), but it seems very coincidental. As far as fuse #s go, I don't see that on #13 or 17 but I see a "Data Link Connector (DLC)" on fuse #5 in the interior fuse panel.

 

[koda2000]

As far as I know, your check engine light must be working too pass emissions. It's something they check for. The bulb is apparently out. I had this happen on one of my trucks. When I removed the instrument cluster to remove the bulb I noticed that Ford populates all the bulb sockets, even for things your truck may not have. I didn't have 4wd, so I switched that bulb for the CEL bulb.

As far as your scanner not connecting, as said check it on another vehicle. As far as why you failed, it was because your CEL bulb was out. I've heard of other's here having a problem not getting their scanners to connect and as I recall they had a fuse out, but I don't think they're connected (the bulb and diagnostic port).

 

[Kevin Ball]

check your fuse, panel is on side of dashboard between drivers door. its the same fuse as cigg lighter. its a 25 or 30 amp fuse. your owners manual will tell you which one. sometimes plugging in a cell phone charger will blow the fuse

 

[fast_dave]

KODA 2000 is onto something, and Kevin Ball added to Koda's hunch!

I too remember someone posting about this problem a loooooong time ago and reading that the cigar lighter fuse affects the OBD port!

Did a quick Google search and came up with this:
CEL came on, OBD II port dead

 

[Austin Healey]

SOLVED, maybe. Checked the fuse (#7 for the OBD circuit on my '97, which doesn't share a circuit w/ anything else (different from earlier models, apparently). Fuse looked OK, but light corrosion on the legs. Wire-brushed, replaced fuse and scanner worked fine. (A lot of times, simply pulling and replacing a fuse will scrape light corrosion off the fuse and socket, even without wire brushing).

HOWEVER, I'm still somewhat suspicious. The reason is that when the OBD wasn't working, there was still power to the under-dash connector to activate the scanner (it just couldn't connect). If the fuse was the problem, why would there be power to the OBD connector? So I'm still concerned that this may be an intermittent problem, with my "fix" just being coincidental. But, if it stays fixed long enough to pass emissions, I won't have to worry about it again for two more years.

Also, just noticed earlier post in this thread about the DLC circuit. If my Explorer has it, I'll check that too.

 

[fast_dave]

Austin Healey,

Legitimate SMOG Shops will work with you.

DON'T pay for a smog test until you do the following first!!!!

Tell them your Ex's problem, and ask them to take a minute hook up a hand-held portable scanner to your OBD port so that they can check for "the handshake/communication" - legit shops will do that for free.

Most if not all smog shops have a portable scanner so as to check if a vehicle has made the minimum amount of "drive cycles" that are requires to perform a complete smog check. In your case, it can be used to check two-way communication.

Hope that helps, Merry Christmas, and report back!

 

[J_C]

If the fuse was the problem, why would there be power to the OBD connector? So I'm still concerned that this may be an intermittent problem, with my "fix" just being coincidental.

While I don't know if this is what happened, there is a possible explanation. If you have contact corrosion, whether it be on a fuse and/or the fuse box contacts, or anywhere else, you might be measuring 12V there with a multimeter, but once you start passing current through that corrosion it acts as a resistance and drops voltage. Similar happens when you have a corroded battery terminal and the vehicle gets 12V but struggles to start.

If that were the case, a test for that would be to use a resistor between the port power pin and chassis (or data link connector) ground, a resistor value you estimate to be about what the scan tool was using. For example you could ballpark 100mA (which is probably too high but not excessively so in the context of a vehicle electrical system so it would work). 12V/100mA=120 ohms (Ohms law). A 120 ohm resistor between the data power pin and ground should result in a multimeter voltage measurement at the power pin of near enough to 12V still.

Again this is just theory, but one thing I would do is take a piece of notebook paper, cut thin and folded to the shape of the fuse contacts, and push the fuse in and out with the paper on the fuse blades to try to clean a little oxidation off the fuse box contacts. It would work even better if the notebook paper was saturated with brasso or similar metal polish during the insertions, then flushed out with spray contact cleaner, but since all the above is only theory it might be excessive to do that much *yet*. Going one step further the whole fuse box can be pulled and the contacts pulled out the back for cleaning but I hate to add that stress to old wiring unless absolutely necessary.