Question about Fuel Trim Condition and ABS/TRAC/VSC Warning - 04 Rav4

Scott Diagnostician Claremont, California Posted   Latest  
Question
Driveability
Chassis
2004 Toyota RAV4 2.4L (2AZ-FE) 4-spd (U140F)—JTEGD20V840022470
P0171 - System Too Lean Bank 1
C1201 - Engine Control System Malfunction

Customer states that the MIL, TRAC OFF, VSC and ABS lights came on the dash (at the same time). No driveability concerns. Check and advise. Vehicle mileage: 234000

We performed a health check and this is what we saw.

Here is the P0171 FF

And the C1201FF

We looked up the Diagnostic Procedure for the C1201 and this is what we found in TIS

Although we found DI-600, reading the circuit description, they're claiming that a PCM failure (Fuel trim DTC we presume) is what set this DTC although the FF data doesn't agree with the P0717. At this point we cleared all the DTC's and road tested the vehicle. We then began to investigate the P0171 and checked the following:

Vacuum/air intake leaks: None found. 

Fuel pressure: 51PSI - Spec is 44-50 PSI

This vehicle is equipped with an AFR sensor and we checked the tailpipe lambda using a Bosch LSU4 sensor. With commanded .998 Lambda we measured exactly the same and various loads in gear standing still. TFT's were high (18-22%) with lambda measured at the tailpipe equaling commanded so we feel confident that the AFR sensor is ok.

Check MAF sensor operation and failed it. After replacement, we road tested the vehicle extensively and all monitors have run and completed. We rechecked fuel trims and for the most part we're happy with the reduction but during QA we logged TFT and found 13% at medium to heavier throttle. We're going to recheck a few things but I'd like to hear from anyone who's encountered something like this and get their opinion on the matter. 

Shall we ship this or keep investigating? What are we missing?

What's your input on the C1201?

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Chris Diagnostician
Commack, New York
Chris
 

I wonder what happens when you put it into check mode and drive it from cold and then let it idle. What does the fuel pump look like While this is happening? I wonder what the rpm of that pump is.

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Scott Manager
Claremont, California
Scott
 

I can ask my tech to do this tomorrow and report results. As for the pump, I reported our test results to your response below.

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Geoff Diagnostician
Lahaina, Hawaii
Geoff
 

C1201 is the traction system saying "I quit, until you go and fix your engine". It will set again if the CEL comes back. The higher fuel trim is likely dirty injectors given your mileage. Most of what I know I learned from your FIRST web site, btw. :-)

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Scott Manager
Claremont, California
Scott
 

Yeah I was thinking about the injectors, they may be dirty or starting to loose their linearity. We have a flow bench we can verify that with. It’s amazing to see that the injectors can flow evenly at certain frequencies and then flake out at others. When that happens the only repair is replacement. Thanks for your input. Since the sun is still up for you can you take a nice profile pic and

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Geoff Diagnostician
Lahaina, Hawaii
Geoff
 

Sunset is at 6:45 :-) I didn't see how/where to add the pic, I will have to look at it again.

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Scott Manager
Claremont, California
Scott
 

When logged in click on the GW tile upper right to get to the settings page Geoff.

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Geoff Diagnostician
Lahaina, Hawaii
Geoff
 

SCOTT: Thanks, Found it. Now....is there a way to only get emails for NEW threads in our selected interest Topics, not an email EVERY SINGLE time somebody posts? The emails are getting crazy. And it'll get worse as more people join in. Don't wanna turn off all mail but I'll have to soon.

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Scott Manager
Claremont, California
Scott
 

Hi Geoff, Go back to the setting page and check on the notification and watching options.

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Glen Owner/Technician
Arthur, Illinois
Glen
 

Isn't the C1201 set because of the ECM DTC's?

+2 Ð Bounty Awarded
Steven Mechanic
Spokane, Washington
Steven
 

The C1201 is only set because of the fault with the engine control. The VSC/ABS system needs to be able to work with the engine to reduce power during certain events, but if an engine fault is present, then it may not be able to. As the fault description says, check engine dtc's. That's all there is to that. For the slight lean issue, was it an aftermarket MAF that was installed? Have you

+2 Ð Bounty Awarded
Scott Manager
Claremont, California
Scott
 

Thanks Steven, On the C1201, why doesn’t the FF align with the engine controller‘s FF? In regards to the MAF, all factory configuration and parts. I understand and have witnessed what happens to the transfer function when airflow before or after the MAF changes due to mods. Airflow measurements before and after replacement were checked and we definately improved our numbers.

+1 Ð Bounty Awarded
Glen Owner/Technician
Arthur, Illinois
Glen
   

I don't think I ever checked the FF on a C1201 when I have ECM DTC's. Are you saying they usually match when the C1201 is an information only DTC's

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Scott Manager
Claremont, California
Scott
 

I’ve never experienced this DTC before and figured that if they were both triggered at the same time the data would closely match but I see that’s not the case.

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Steven Mechanic
Spokane, Washington
Steven
 

I don't know why the FF's don't match. I would chalk it up to how the module is programmed. I've seen lots of things that don't make sense when working on German cars. Add in the fact that the shop I work at only has Alldata and Identifix, and you can see how I have to work in a world of confusion on a daily basis. When diagnosing, I like to keep moving forward without getting sidetracked by

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Scott Manager
Claremont, California
Scott
 

Thanks Steve, See my comment on the injector frequency, speed vs. on time, I’ve seen some bizarre behavior and this may be what’s causing the condition we’re observing.

+1 Ð Bounty Awarded
Steven Mechanic
Spokane, Washington
Steven
 

That's interesting. I never thought about it that way. Thanks!

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Scott Manager
Claremont, California
Scott
   

We shot a video of a real bad set of injectors (they were Aftermarket Bosch Look-a-likes) and we had one genuine (green) one in there as a comparison. The flow bench is the ASNU New-Digital unit that has an auto cycle that simates various engine speeds and injector on times. If you can get past the horrendous fuel pump sound, you can pick up the various frequencies as the test progresses.

+3 Ð Bounty Awarded
Steven Mechanic
Spokane, Washington
Steven
 

Testing at the proper frequency and on time. That's the way to do it!

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Jim Curriculum Developer
Frederick, Maryland
Jim
 

Great demonstration. Now I would love to see the current flow to each unit for comparison. One would think the signatures would show some shenanigans. Yes, that is an awful noise.......

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Chris Diagnostician
Commack, New York
Chris
 

I had the same exact vehicle, with the same exact engine do the same exact thing to me. I current ramped the fuel pump and it was screaming 8000 rpm at idle. Maintained great pressure though. I assumed the pressure hose was cracked inside the tank. Unfortunately, the top of the tank was so rotted that any further exploration would‘ve meant snapping all the flange bolts and replacement of the

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Scott Manager
Claremont, California
Scott
 

We did check the pressure under heavy power brake load and subsequently checked the rest pressure for bleed off and it passed the OE spec, so we don’t feel as if we have a pump or plumbing issue.

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Steven Mechanic
Spokane, Washington
Steven
 

I'm interested in your AFR sensor you put in the tailpipe. I've been thinking about building something like this with a digital gauge attached. Do you have pictures of your setup? Does it seem to give you reliable results by putting it in the tailpipe?

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Scott Manager
Claremont, California
Scott
   

I’ll see if I can get one of my guys to snap an image or two tomorrow as I’ll be traveling. The unit is a Motec PLM adapted to a Superflow tailpipe adapter with an airflow Venturi. I tried to find it on their site and I cannot, so therefore no link. I have this unit set up with an analog out to my chassis dyno and I’ve found the accuracy spot on.

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Steven Mechanic
Spokane, Washington
Steven
 

Wow, that sounds a lot more sophisticated than what I was thinking about doing. I was going to buy a cheap AFR gauge and sensor, hook a power supply to it, and put it in the tailpipe. Not sure my idea would work 🙂

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Scott Manager
Claremont, California
Scott
   

Here’s another option you might want to check out.

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Steven Mechanic
Spokane, Washington
Steven
 

Ok, I just watched a video about it. I see what's that's for now. Thanks.

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Bill Technician
Rosetown, Saskatchewan
Bill
   

I have 2 of those innovate with a daytona wego IV dual display. I had to put leads for battery hook up and bought extra extensions for the sensors. If you deal with fancy exhaust these guys could make marks unless you protect​ ​the exhaust. They also fall out from time to time. I will be modifying mine at some point.

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Scott Manager
Claremont, California
Scott
 

Hi Steven, I couldn’t find the link to this device on the Superflow website but you could call them and ask. I took a couple of pictures of the tool so you can see what this device looks like. One Two Tailpipe adapter

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Steven Mechanic
Spokane, Washington
Steven
 

Ok, so it looks like this thing draws exhaust gas out of the tailpipe and across the sensor. I've been wanting to make something like this. Sounds like a good project when I have time. I could buy one, but I don't want to 😁. You know, I bought one of those Hecat cooling system pulsating flush tools, which works great. Then a co-worker looked at it , copied the design, and he made his own, and

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Adrean Diagnostician
Bakersfield, California
Adrean
 

My input on the c1201 . Is just the engine has a malfunction, so The abs sets a code due to it not being able to perform properly until the engine problem is fixed . And yes keep investigating . Did u do a VE test with the scan to see how to trims follow ?

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Scott Diagnostician
Claremont, California
Scott
 

Thanks Adrean, Due to the input from you and the others the C1201 is due to the MIL source. On the VE test, yes we did and this is what we saw.

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Rick Technical Support Specialist
Saint Charles, Missouri
Rick
 

1201 is Toyota's Brain Teaser to make sure you fix the engine operating system first. I use this code in my abs class as a tech strategy builder. I would love to compare (graphing) the MAF and Injector pulse width with a similar known good engine. High mileage vehicle. Where is the incoming air miscalculated at 2200 rpm??? Look closely at intake plenum to and from MAF?

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Scott Diagnostician
Claremont, California
Scott
 

Hi Rick, I guess I haven't had the pleasure of being entertained by the level ambiguity Toyota offers in this case. Isn't the FT correction offering the same intel? Cylinder air is the equation the PCM is after and I agree it would be nice to see a similar one to compare. However, I'm leaning towards non-linear behavior of injector flow rate vs frequency leading to this condition. The MAF

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Tanner Instructor
Wellford, South Carolina
Tanner
 

On Toyota’s generally the abs system will always set that code with a code in the pcm. It is a strategy toyota has used for some time. I like to use the calculation for theoretical maf value and compare that to actual. Normally I find a bad or dirty maf by doing this. After the problem is fixed I like to re run the test and then run a v/e test to confirm that the maf is correct and the engine

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Randy Analyst
Denver, Colorado
Randy
 

The answer to your freeze frame is in documents 1968.2 an j1699. FF can be written at time of pending DTC and must be written within 10 seconds of the time the DTC was set So that is likely when the p0171 FF was written. Your C1201 was set at the time of the second failure of p0171 which caaused a different FF. BTW, I just asked one of the engineers on the j1699 committee if that was correct and

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Scott Diagnostician
Claremont, California
Scott
   

Thanks for the input Randy, for reference, here is the link to the CARB document referenced and here is the section. Yes looking at the TFT avg and the graph tell different stories and there may no longer be a problem. On the fuel quality, we pulled a sample during our analysis And didn’t find excess alcohol. We also noted that the fuel level was low and filled the tank with fuel from a local

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Randy Analyst
Denver, Colorado
Randy
 

FYI, there’s a newer version but that version works for this discussion. Also, there is a proposal to set separate ff for pending and confirmed dtc. I’m not sure how valuable that is though.

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Scott Diagnostician
Claremont, California
Scott
 

Update: We advised the customer to put the vehicle back in service and return in 2-3 weeks for a followup check. I appreciate all the great feedback and I plan to report back with an update in this thread.

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Randy Analyst
Denver, Colorado
Randy
 

Smart move. Totally coincidental but I listened to a Toyota engineer present data today on how they can go to 87% Fuel correction before they exceed emission limits on ffv. This is not in a production vehicle but gives you insight on the lack of benefits to chasing a 10% shift can be.

+4 Ð Bounty Awarded