Code 26 (1 Viewer)

[Brentbba]

Truck thru code 26 this afternoon. Just did the breather extension terminating right behind the fuse block in the engine bay. Could I have knocked something to throw this code.

Truck has a horrible historyof eating O2 sensors, and this is one of the options for this code.

Somewhat urgent as we're headed to Norcal to move my daughter in for school in two weeks.

Perhaps related question - canister next to the fuse block has a hose coming outo the bottom headed under the fuse block and is just laying on the wheel well terminating back by the cab. End of hose is very dusty inside and out leading me to believe this is where it's supposed to be. Onlyh noticed it playing around with the routing of the diff breather extensions. Is this where it's supposed to be or is it supposed to be attached to something? Can't post pics of the hose until new camera is delivered by the brown truck.

Edit: Canister hose per the FSM out the bottom just looks like a vent???

History on the O2's with the truck...long time ago one dealer f'ed up the sensor wires and different dealer found and spliced the wires to one of the two sensors. My gut is telling me that those splices may be failing causing this code in the circuit. Is this wiring harness even replaceable or am I just best off trying to redo the repair. The initial repair was years and years ago!

 

[MoJ]

I'd verify the sensors via the test procedure in the FSM. All you need is your multimeter to check the resistance at the sensor. If that is good there's a flowchart listing a couple of additional places to check it at the diagnostic plug on the firewall. I just went through the same thing on my 94 a few weeks ago. Obviously the splice would be suspect as well.

 

[GeoRoss]

The hose you are seeing is the inlet line for the charcoal canister. That is normal.

 

[Brentbba]

I'd verify the sensors via the test procedure in the FSM. All you need is your multimeter to check the resistance at the sensor. If that is good there's a flowchart listing a couple of additional places to check it at the diagnostic plug on the firewall. I just went through the same thing on my 94 a few weeks ago. Obviously the splice would be suspect as well.

So you're testing resistance on the molex connector on the sensor side if I'm following - right? What should the readings be? Not an electrical genius here. Last time I threw a 26, I ran the two tests in the FSM. Followed the test procedure and got nothing more back on that. I'll look for the flowcharts you mention.

Can I test the resistance on the truck side of the wiring harness while I'm down there too?

Thanks for your help.

I'm going to gently pull off the electrical tape the stealer put on the splices and see if they are still even viable. I'm sure I'll find nothing but twisted together wires. I doubt the took the time to either solder or crimp the wires together. I'm concerned about how brittle the wires will be after 15 years near such a heat source as the exhaust pipes!

 

[MoJ]

The splice would be easiest to check first (and most suspect imop).

Yeah, you start at the molex connectors for each o2. The resistance should be 5 to 6.5 ohms between +B and HT when the truck is cool. (+B is the left hand lead if the snap portion of the connector is at 12 o'clock.) If that passes you check VOLTAGE at the diagnostic port as described below. When you follow the flow chart you'll need a buddy to hold the RPM's for you. Also, when checking at the diagnostic port be sure you get a good contact with the probe tip...it was a little tough getting it in there just right. Edit: The SST mentioned is of course just a paperclip.

1994 FSM Page EG-315-316

 

[80t0ylc]

Excuse me, but a 26 is "Air - Fuel Ratio Rich". While it could be 02 sensors, FSM calls out possible trouble areas in this order:

Engine ground bolt loose
Open in E1 circuit
Injector circuit
Injector
Fuel line pressure
ECT sensor
Compression pressure
ECM

 

[Brentbba]

Moj - thanks for this - my daughter is in town and we took her to dinner last night - didn't have time to pull the FSM to look for what you posted above. I appreciate that and your time to do so.

80t0ylc - I know, it's just that my truck and '94's have a terrible history of eating O2 sensors like candy.
The open in the E1 circuit is likely the splice I mention.

Where is the engine ground bolt - no idea. After 15 years of rattling around, I may as well check that to. Torque specs on it too if you know?

 

[80t0ylc]

......Where is the engine ground bolt - no idea. After 15 years of rattling around, I may as well check that to. Torque specs on it too if you know?

I can't find it in my hard copy FSM. Someone might be able to search on it if they have a soft copy (downloaded). Torque = ? If you find it, pull wire off & clean terminals & metal w/solvent & reinstall w/ star type (biting) washer for good contact. - My .02

 

[Brentbba]

I can't find it in my hard copy FSM. Someone might be able to search on it if they have a soft copy (downloaded). Torque = ? If you find it, pull wire off & clean terminals & metal w/solvent & reinstall w/ star type (biting) washer for good contact. - My .02

I've never found it in my FSM either!

Good news and bad news on the tests tonight.

Good news is that both O2 sensors test ok on the Ohm meter for resistance

Unwrapped all the electrical tape on the DS harness where the splices were repaired years ago. Damn they did wrap it well.

It looks like they repaired all 4 wires in two places, once fairly close to the molex connector and again up above the drive shaft.

Bad news is that one of the wires above the drive shaft has a blue outer sheathing with some wire inside that and then an inner white sheathing with another wire. This is the only wire I took the innermost electrical tape off of because I noticed the outer wire loose. The inner wire IS soldered, so that's a good sign. The wire in the outer sheathing has come loose and doesnt' look like it was ever soldered with the inner wire. What's perplexing about this is that the wire that this one is connected to on down to the molex connector is white, but no outer blue sheathing for that outer wire to connect to. This puzzles me and I wonder if this outer wire may be causing an open E1.

I'd take a pic, but my new camera is with Mr. Brown Truck and won't arrive until Friday.

Any thoughts?

Don't know whether to simply connect the outer and inner wires together or leave the outer wire out of the picture because it certainly does not continue to the connector.

Didn't have time to run any of the other diagnostic tests this evening.

 

[Brentbba]

Moj - one more question if you dont' mind. If I'm reading the diagnostic steps correctly, you've got to have the paper clip and the volt meter prob stuck down in E1 at the same time? Tight fit!

Will be doing the volt tests this evening if I can get out of work a little early.

 

[MoJ]

You wouldn't need to have both of them shoved in there at the same time, just in contact with each other.

I'm laughing at myself remembering having my wife hold the RPM's at a roaring 2500, me holding the paper clip and probes in place, counting the voltage flunctuations, watching for 10 secs on a stopwatch, all while sweat dripping off my forehead in a 90 degree garage.

 

[Brentbba]

LOL! Kind of thought all you'd really need to do would be touch the paper clip for the E1 side and put the probe in the other side. Thx - an electrical genius I'm not, but I can do simple stuff.

Well, my truck won't fit in the garage anymore! By the time I get home from work the temp near the coast will be a balmy mid 70's this evening.

Had to get a cheap volt meter as the multimeter I own is digital and according to my FIL (electrical engineer) the digital wouldn't work counting the flucuations as described in the FSM! $10 at Home Despot got me an analog multimeter. May just keep that one in the truck!

 

[MoJ]

Had to get a cheap volt meter as the multimeter I own is digital and according to my FIL (electrical engineer) the digital wouldn't work counting the flucuations as described in the FSM! $10 at Home Despot got me an analog multimeter. May just keep that one in the truck!

Oops I used a digital. It showed the fluctuations but maybe that's only for my Harbor Freight model. I can see where the analog needle would be a lot easier to keep an eye on.

 

[Brentbba]

The FIL said the digital takes samples for the readout vs the analog seeing the needle jump. For $10 it's worth seeing the needle if I'm counting volt surges.

Wish I could figure out that blue wire on the truck side harness. Any chance of you taking a look at the inner harness wiring to see what color wires you've got. It's the inner sensor harness that runs up by the drive shaft and disappears into oblivion up in there. Curious to see if you've got one blue wire that runs all the way to the connector or if it's white. Can't remember the other three colors off the top of my head. If you can't, no biggie. Have a pm into CDAN on the specifics of the wiring harness.

 

[Giulitto]

I just threw this code plus a code 25. Now I don't have an FSM, I just have a Haynes manual. It give multiple reasons for these codes. Yet when reading further into the book if a O2 sensor had gone bad I would have received a code 52 IIRC. One of the possible areas that it list, could be in the EGR. I was intialy throwing a code 71 until I reset it which was in the EGR system. My O2 sensors were replaced about three years ago.

 

[MoJ]

Wish I could figure out that blue wire on the truck side harness. Any chance of you taking a look at the inner harness wiring to see what color wires you've got. It's the inner sensor harness that runs up by the drive shaft and disappears into oblivion up in there. Curious to see if you've got one blue wire that runs all the way to the connector or if it's white. Can't remember the other three colors off the top of my head. If you can't, no biggie. Have a pm into CDAN on the specifics of the wiring harness.

I think this is what you're asking:

Inboard sensor. 4 wires on each side of the connector.

O2 sensor side / truck side

Redish / yellow with red stripe
Grey / black
White / orange
Blue / white

Someone correct me if I'm wrong but I think all 94's were 50 state smog so it shouldn't be any different for a CA truck.

 

[Brentbba]

Correct,

That blue white wire. Does it have an inner white and outer blue sheathing (if you can even tell) and does that extend all the way to the connector? Mine is a two part wire. The inner white portion goes all the way to the connector. The wire in the outer portion covered in blue stops at the first splice in my truck side harness. I'm thinking that the outer wire should go all the way to the connector as well and it doesn't as a result of the splice. Easy fix to reattach the wire in that outer sheating at the splice.

Thanks for your help!

 

[MoJ]

Ahhh OK, I see what you're talking about.

It appears to be the same on mine...I guess you'd call it a coaxial setup, like an antenna coax with an inner core wire and outer shield/ground. I didn't even notice it until I pryed apart the black corrugated wire loom. Coming from the truck side it's thicker blue wire all the way until about 2 inches before the o2 connector. It then transitions to just the inner white wire which is the only one going into the connector. I can even see a few silver frays from the outter wire where the transition takes place. I can only assume that the outer portion is designed to shield the inner wire from interference along its path and doesn't carry a signal of any type.

If that splice is otherwise not corroded and is providing a good connection it sounds like you may have ruled it out.

 

[Brentbba]

AWESOME!!!!!

Thank you soooooo much for your time crawling under your truck and looking!!!!!

It does rule out that wire as being an issue and probably all the splices. They look pretty good.

 

[Brentbba]

Damn...I think.

I buttoned up the wiring harness. Kept the outer sheathing wire away from the white wire splice when I wrapped it all up.

Before doing this I'd done another code test and got the 26 as expected, but got a 28 because I hadn't plugged the inner O2 sensor back in yet.

Pulled the EFI fuse to clear the codes, plugged the sensor back in, harness all buttoned up in new electrical tape and wire loom and took the truck for a drive to get the CEL to come back on so I could perform step 3 of the diagnosis tests above.

Truck ran a little rough in the beginning, but I'd expect that just from pulling the EFI fuse - ECM relearning. Damn if about 10 minutes into the drive the truck was idling like she was brand new. 600 RPM w/o any flucuation in the needle at all! Kept driving and the CEL NEVER came back on!

I don't know if that outer wire was just causing an intermintent problem or not. I've had the Code 26 before, cleared it and it wouldn't come back. Go Figure!

Given the upcoming road trip, driving the truck to work today and tomorrow to see if the CEL will reappear. Damn, I hate intermitent problems like this. At least I know both O2 sensors are still ok and that the splices really were soldered and not just twisted together. Feel better about both those items.

I'd still like to find out where the engine ground bolt is to make sure it's tight. Anyone? I can not find any mention of it anywhere in the FSM.

Moj - thank you for all your help!