Cel 12, 25 & 26

[Seth_O]

I recently did a head-job on my '93. All factory parts, and had the head machined at a reputable shop. Only had one hiccup upon reassembly (getting the exhaust all snugged down in the correct order to be leak-free) but got it resolved and running smoothly.

Shortly after I popped a CEL. When tested I had three errors:

12: Knock control sensor
25: Air-fuel ratio lean
26: Air-fuel ratio rich

Ive cleared the codes several times, and sooner or later they always come back. All three of them together. I cant see how these would be related?

Any ideas? Search yielded only one other person with these three in conjunction and there was no resolution.

 

[Jgrauman]

Timing set correctly?? Could be unrelated. 25&26 can come from exhaust leaks. If your timing is off could cause detonation

 

[bigredmachine]

25/26 is most likely due to a leaky exhaust or the o2 sensors are no good. you should test your o2 sensors at the obd port under the hood.

12 id check the wire harness going to the sensor make sure that something didn't get pinched or crunched when removing the head

 

[Seth_O]

Timing set correctly?? Could be unrelated. 25&26 can come from exhaust leaks. If your timing is off could cause detonation

Good idea on the timing, I havent checked it since it was running just fine. I have noticed i am getting ~10% worse mpg, those could be linked.

 

[Seth_O]

25/26 is most likely due to a leaky exhaust or the o2 sensors are no good. you should test your o2 sensors at the obd port under the hood.

12 id check the wire harness going to the sensor make sure that something didn't get pinched or crunched when removing the head

I wasnt aware there is a way to check the O2 sensors at the OBD port? Its OBDI.

From what I can tell there is no standalone RPM or knock sensor, that signal comes from the dizzy.

 

[bigredmachine]

I wasnt aware there is a way to check the O2 sensors at the OBD port? Its OBDI.

From what I can tell there is no standalone RPM or knock sensor, that signal comes from the dizzy.

ill see if I can pullup the inspection for the o2 sensors.

you have 2 knock sensors on the block one towards the front of the engine near the coolant temp sensor and the other on is on the same side towards the back

 

[bigredmachine]

knock sensor inspection

 

[bigredmachine]

o2 sensor inspection

 

[Seth_O]

Thanks bigred! I am going to check those out this weekend.

 

[bigredmachine]

no problem, if one of the o2 sensors fails you should replace both at the same time. denso are preferred, I have ngk in the truck at the moment and they have been working fine for over a year

 

[RobE30]

I love stumbling across helpful threads. Thanks @bigreadmachine

 

[Rifleman]

Toyota had a factory recall on the 93 and 94 O2 sensors with free dealer replacement if they were bad. So before you buy any sensors you might want to check, and see if that recall was ever done on your truck. Here is a Link to that factory recall info.
http://www.risingsun4x4club.org/uploads/Snowrun/1994 fzj80/1994 Repair manual/Service bulletin/T-CP-SO2-0162-W.pdf
If it turns out that you need new O2 sensors you should think about going with the Toyota sensor kit listed in the recall info. When i did this repair the cost of the factory sensor kit P/N 89465-60110 was a little less expensive then buying the aftermarket Denso sensors.

Plus the factory kit comes with new gaskets and new sensor lock nuts shown on the left side of the photo below. The cat gaskets and lock nuts on the right side of the photo are not included in the kit, but you'll need them too, to do the job. When you do this job, spend the extra money for 4 new head pipe studs not shown in the photo, trust me you'll thank me later for that tip.

Note, some people are able to replace both of their O2 sensors without removing their cats. In my case that was a no go, due to the fact that the factory O2 sensors lock nuts were completely eaten away, to the point they had no flats left on them to put a wrench on. So in order to remove those nuts, i had to drop my cats to clamp a set of vice grips on them, in order to remove them.

 

[Seth_O]

Found out why I'm getting a CEL 12:

 

[Seth_O]

Of course, in the process of fixing that, my coolant temp sender connector disintegrated.

Anyone have a PN for that connector?

 

[sswong98]

Hello Seth,
I have 1994 L/C and throwing codes 12 & 26 (comes on and off). Could you please share as to which broken connector you are showing in your hand? I have changed out my o2 sensors last year. I wished I knew about the recall. Also, I recently replaced the plugs and distributor cap/rotor. My L/C runs great, just throwing the codes. I did notice my air intake hose has a split when I removed to get to the plugs. I don't know if that occurred while changing the plugs or happened before hand.

 

[Seth_O]

Hello Seth,
I have 1994 L/C and throwing codes 12 & 26 (comes on and off). Could you please share as to which broken connector you are showing in your hand? I have changed out my o2 sensors last year. I wished I knew about the recall. Also, I recently replaced the plugs and distributor cap/rotor. My L/C runs great, just throwing the codes. I did notice my air intake hose has a split when I removed to get to the plugs. I don't know if that occurred while changing the plugs or happened before hand.

That was the front knock control sensor. Right beneath the intake manifold and tucked up kind of by the PS pump. Surprisingly I was able to get to it w/o removing much of anything else.

 

[MoJ]

Hello Seth,
I have 1994 L/C and throwing codes 12 & 26 (comes on and off). Could you please share as to which broken connector you are showing in your hand? I have changed out my o2 sensors last year. I wished I knew about the recall. Also, I recently replaced the plugs and distributor cap/rotor. My L/C runs great, just throwing the codes. I did notice my air intake hose has a split when I removed to get to the plugs. I don't know if that occurred while changing the plugs or happened before hand.

Tightly wrap the intake hose with duct tape. Reset the codes and see if they return.

 

[sswong98]

Hello All,
I tried looking for the same connector, but looks like everything under intake looks fine. I see two connectors going into the engine just above the oil filter. I am guessing one is the coolant temp (1 o'clock) and the other might be the knock sensor (11 o'clock). I also took MoJ's advice and tape the intake hose. and reset the code. I drove around the city a little over 12 miles and so far no code. I'll test drive more and report back. Thank you all for your help.

 

[Seth_O]

That's good news. A split intake hose is one of the most common Cel12 causes. Likely culprit for unmetered air.

Not sure where you're at, but FYI - in CA any kind of tape on the intake is an immediate emissions fail (for visual.)

 

[sswong98]

Hi All,
Drive around all weekend and no code. I do live in Calif, so you are correct, tape around the intake will not pass smog. I ordered a new hose and should arrive next week. Thanks all for the help.