Do the OBD #'s add up?

New to me 2000 Tacoma 3.4 manual. CEL was lit when I bought it, so came home and replaced air filter and plugs [

$50 PK16TR11 / 3289

PK16TR11] and sprayed a very dirty MAF with the preferred CRC. Ten minutes after restart the CEL it up again. Code reader at Advance Auto says "P 1130 A/F Sensor Circuit."

Nefore I buy the pricy A/F sensor, could some of you Toyota tec's take a peek at the other OBD data to confirm that this part is the most likely weal link in the system? Here are the scanned values, taken at idle, 40 degrees ambient temperature:

throttle position

 

tps 8.6
rpms 700
calc load ~15
MAF ~0.5
coolant 185
iat 53
ign adv 15
short trim 0-2
long trim 5.5-6.3
fuel sys1 closed
O2 s12(v.) ~.240
O2 s11 ~3.3
eq ratio 11 ~.995

From my experience rebuilding and adjusting a 2000 Cherokee 4.0, these fuel trim #'s look pretty good. I have no frame of reference for the O2 values that follow. The truck starts and runs smoothly, even better since new plugs went in. The old plugs are a uniform tan at the electrode, and all were worn to about .075.

So do I need to replace the A/F sensor and is that likely to end the CEL episodes? Naturally I will post follow up reports.

tia,

4toys [not even considering mods until CEL is gone and all fluids exchanged]

2000 3.4 manual TRD 4x4

 

As far as the OBD test goes, it would have been good to do a short drive and read the results, but this seemed too unsafe so didn't happen.

Having read a few articles on OBD results on the 3.4, it seems likely that the observed voltage for the O2 sensor [same as air-fuel?] is too low. This article...

http://www.4x4wire.com/toyota/4Runner/tech/OBDII_ECU/

...suggests that an average voltage of .475 is optimum for the O2 sensor. Mine reads an average of .240 at idle, and I guess this sensor should be pretty much in the .400 to .550 range all the time.

Looking under my 2000 50-state Tacoma, I see what appear to be 2 cats with a sensor just ahead of the front one. I couldn't see any other sensor further back after the cats. So is the one I saw, which is directly above the front anti-sway bar, the one to replace? Assuming the correct part is Denso 234-9003.

As the song says, I've been wrong before. Awaiting confirmation or ...

4toys

 

You are in VA so assuming you don't have CA emissions, your A/F sensor is this one according to RockAuto. For my 2003 manual 4x4, the 9003 was the correct sensor, but RockAuto listed this one for your 2000.

DENSO Part # 2344161 OE Style; Includes Gasket
Upstream; 4WD; Standard trans.; Except California Emissions

 

Sticker under the hood says Calif. compliant and it has 2 cats, so probably should call a dealer with my VIN to be sure.

Thanks for responding. Do you agree with my somewhat sketchy analysis of the problem?

Re: your sig. My son-in-law was at Denny on Nov. 9 and couldn't stop talking about it until the 30th. And he's a Virginian, too. Go figure.

4toys

 

yeah, it sounds like the A/F sensor could be the culprit.

Re: Denny on Nov. 9, those games are always interesting, even if they don't turn out the way I want

 

Or the sensor could be doing its job and there is an actual problem.

 

Rich91710 wrote: "Or the sensor could be doing its job and there is an actual problem."

Yeah, before I bought the truck I checked the code history, which had a few more 1130's as well as some 1135's [A/F sensor heater malfunction] and one 0125 [insufficient coolant temp in closed loop]. After reading all codes, I cleared history. Previous owner replaced the thermostat and water pump earlier this year, which probably accounts for the 0125. At any rate, neither of those other codes has come back.

At a guess, a problem other than the sensor itself would most likely be an air leak or fuel delivery issue. My elementary awareness of A/F control parameters leads me to discount that possibility, since OBD shows MAF within expected range at idle, coolant temp close to optimal, and combined fuel trim under 10%. Further, the truck starts, idles and runs pretty smoothly, and spark plug inspection was unremarkable. Everything I've learned points to a weak, dying Oz sensor heater. Since experience has shown that my limited knowledge might well lead to incorrect conclusions, I appreciate your suggestion.

So, can I disconnect the A/F sensor leads and test its condition?

4toys

 

Sin, u da man!

Does anybody know the differences between the 49- and 50-state emissions systems? Mine has 2 cats but only 1 sensor - Bank 1, Sensor 1, as shown in the drawing. It's apparently 50-state.

4toys

 

All I have is the 1996 Repair Manual. It doesn't show 2 Cats. That info I posted earlier may not apply to your vehicle.

 

When i bought the truck, prev ownr admitted that the CEL was on because of the O2 sensor. He also allowed that there was a rattle in a heat shield that he couldn't locate. Well, it turns out that the rear O2 sensor was sitting loose in its bung, unaccompanied by the usual fasteners.



After tidying up threads and mounting surfaces, I have reattached and am heading to Advance Auto to read codes and see if P1130 revisits.

4toys

 

After a few days' absence, P1130 and P1135 have returned. In the meantime, this owner stays on a slow learning curve: out on the 'net, another 3.4 owner's scan snapshots show both O2s1x readings moving within the expected range. OTOH, my O2s11 stays at a consistent 3.298. Unless I'm way off base, O2s11 is the A/F sensor. At today's reading, O2s12 fluctuated within the normal range

Before ordering a new A/F sensor I will try one more "cure" suggested by a counterman down at the parts store: remove sensor and hit its tip with the flame from a propane torch. He swears that this action somehow "wakes up" old sensors to an active state.

Comments?

4toys

P1130 - A/F sensor circuit range/performance
P1135 - A/F sensor heater circuit malfunction