Wire harness or air flow issue

I have a 2008 Scion xB. It’s been a great car, but I’m starting to have some trouble with it. While my wife was driving it, she experienced an uneven idle (felt like it was about to die, revved up, then repeated that cycle over and over) along with a big loss in overall power. She took it straight to the dealership to have them check it out. They said that the problem was a faulty wire harness based on one of Toyota’s TSBs. I went out and bought a code scanner and found out I have P0101 (Mass Air Flow) and P0172 (System Too Rich) active. I’m not terribly knowledgeable about car repairs, but based on what I’m feeling and what I’ve read, I think I actually have an air flow problem - maybe a vacuum leak? I don’t see how the wire harness problem would cause the uneven idle and power loss. Anyone have an opinion or advice for me?

Here’s some info. from the TSB if it helps:

S-SB-0050-08 November 12, 2008 M.I.L. "ON" DTC P0101, P0172, P035 #, P2237 or P2238 Service Category Engine/Hybrid System

Engine Control


Some 2008 - 2009 model year xB vehicles may exhibit a M.I.L. “ON” with one of the following Diagnostic Trouble Codes (DTCs):
^P0101 - Mass Air Flow Circuit Range / Performance Issue
^P0172 - System Too Rich
^P035 # - Ignition Coil '# ’ Primary / Secondary Circuit
^P2237 - Oxygen (A/F) Sensor Pumping Current Circuit / Open
^P2238 - Oxygen (A/F) Sensor Pumping Current Circuit Low

An improved engine wire harness has been developed and implemented in production to address this condition. Use the following repair procedure to diagnose and repair customer complaint vehicles.
Production Change Information

This TSB applies to vehicles produced BEFORE the Production Change Effective VINs shown.

Parts Information

Warranty Information
^This repair is covered under the Toyota Comprehensive Warranty. This warranty is in effect for 36 months or 36,000 miles, whichever occurs first, from the vehicle’s in-service date.
^Warranty application is limited to correction of a problem based upon a customer’s specific complaint.

Required Tools & Equipment
Additional TIS Techstream units may be ordered by calling Approved Dealer Equipment (ADE).
Repair Procedure
1.Using TIS Techstream check for stored DTCs.
2.Verify one of the following DTCs is present.
^P035 #
NOTE If other DTCs are present along with any of the DTCs listed above, this TSB does NOT apply. Follow Repair Manual procedures to diagnose those DTCs.

3.Follow Repair Manual procedure to inspect the DTC-related component(s).

Refer to the Technical Information System (TIS) applicable model year Scion xB Repair Manual:
4.If the DTC-related component(s) is within Repair Manual specifications replace the engine wire harness.
5.After replacing the engine harness clear DTCs and verify that no DTCs reset. Then warm vehicle to operating temperature and test drive to verify repair.

TSB # S-SB-0050-08 November 12, 2008

This TSB applies to vehicles produced BEFORE the Production Change Effective VINs shown below.


It could be that the computer is getting incorrect signals or no signal from the MAF due to a problem in the wiring harness. If I were you I’d let the dealer replace the harness. If that solves the problem, you’re done. If not, then worry about further troubleshooting. But it sounds like the harness could well be the problem.

I’m off warranty (4yrs/38,000 miles) and replacing the wire harness is an expensive repair. I don’t want to pay for it and immediately be stuck paying for another repair.

Would a signal problem from the MAF cause the uneven idle and lack of power?

These symptoms are common for a fuel mixture problem. There’s a bunch of things that can cause a mixture problem, from a clogged air filter to faulty O2 sensors to faulty injection rail fuel pressure to a faulty to a computer problem etc.

I can’t tell you what to do as I have no specific knowledge about your car or the TSB. Maybe talk to an independent mechanic (not the dealership) who specializes in Toyotas and see what he/she thinks before investing in the new wiring. But if the wring is bad, it could indeed cause the a mixture problem and the symptoms you are reporting.

Also try Googling “Scion Rich Mixture TSB” or something like that. This problem may have been discussed on other car repair forums and Google will find them for you.

Best of luck.

In a different thread someone here pointed out that TSBs are generally repaired at the cost of the brand, even after the car is out of warranty.
It certainly makes sense: seems to me it is their fault. They should replace that harness at their cost. That way, if the problem still occurs, you at least know it isn’t the harness.

If the dealer refuses to fix it under warranty, I would write a letter to the regional manager saying you’re a loyal customer and request that Toyota take care of it under warranty, seeing it is a known problem and an expensive repair, and if they don’t take care of it they may lose you as a loyal Toyota buyer in future, etc. There’s a good chance they will cover the repair for you. Just be polite but firm.

But first, open up the air intake and inspect for rodent nests and debris. Inspect the underhood wiring for rodent damage…then CLEAN the MAF and carefully inspect for vacuum leaks…

@RemcoW : That’s how I feel. I don’t know how they can justify my car being less reliable than one manufactured just a few months later, even if I am off the bumper-to-bumper warranty.

@jesmed : I’ve contacted Scion Customer Care and the service manager at the dealership. The dealership offered to charge their cost for the parts and Scion offered to pay half of the overall bill. That still makes it $500 which seems expensive for a repair on a car this new that has been maintained properly.

@Caddyman : I will do those things. I’m pretty new to DIY car maintenance and repair, so I’ll look for some resources to help me. What do I need to do to inspect for vacuum leaks - just look for punctures or hoses that don’t fit together tightly?

@TubaTwo: I’m assuming you’ve verified yours is one of the car serial numbers affected. And that Toyota never notified you of this problem in writing while the car was under warranty.

Basically what happened is they made a mistake in building the car, didn’t tell you about it, and when it failed, told you that you could have had it fixed for free if you had only brought the car to the dealership before the warranty expired. But you had no way to know because they didn’t notify you. I think Toyota should verify the wiring harness is the source of the problem and if so, should fix it at no cost to you.

Any statement that costs related to TSBs are usually borne by the car manufacturer is incorrect.
Few are unless it’s tied in with a Recall or Campaign.

If car manufacturers assumed the cost of every TSB that exists then everyone on the planet would be on foot because they would have all ceased to be in business long ago.

@GeorgeSanJose: I agree with what you’re saying, but in talking to the two representatives I’ve spoken with from Scion Customer Care, paying half of the cost is as generous as it appears they will be.

This is such an oddball problem that it just doesn’t seem right. I’ve spoken with Scion Customer Care twice and the service manager once. Does anyone have some other strategies I should try to get this resolved? Would it be worth getting a second opinion with an independent mechanic?

Seems kinda hosed, throwing something over the wall that wasn’t ready for prime time because you quickly find out will need fixing. You keep quiet about it to then charge people to fix a problem they couldn’t have circumvented. Maybe not everyone will need the fix because they don’t have the problem - fine.
Your car needs fixing, though.

I’d press them to fix it because it is the right thing to do - maybe it isn’t financially expedient but it should remind them to not toss things over the wall that weren’t ready to be sold. It makes them look bad.
Send them a link to this thread and other forums where you ask the same question, if you think that helps.

I’d certainly think twice about getting that make or suggesting other people buy it, reading this.

Huh, wouldn’t the rich condition affect the emissions and thus be covered by the 70K emissions warranty?

Quoting @Tuba Two: "Would a small claims court see this as a violation of an implied warranty? "


Any advice on where I should go from here? Would you recommend continuing to fight with customer care (I don’t need it fixed right away because I can bike in the summer), taking their offer to pay half, getting a second opinion from an independent mechanic, or resetting the codes to see what happens? I assume that if the problem goes away after resetting the codes I can feel fairly confident that it is an electrical problem.

@Bing said:

Huh, wouldn't the rich condition affect the emissions and thus be covered by the 70K emissions warranty?

I live in North Idaho where there are no emissions laws. The warranty booklet says that the emissions warranty only applies where there are EPA approved standards.

From the warranty booklet:

Some states and localities have estab- lished vehicle inspection and maintenance (I/M) programs to encourage proper vehi- cle maintenance. If an EPA-approved I/M program is in force in your area, you are eligible for Emission Performance Warranty coverage.

Also, I don’t think the emissions warranty would apply to the main engine wire harness. Here are some other excerpts from the warranty:

This warranty is in effect for two years or 24,000 miles from the vehicle’s in-service date, whichever occurs first. Additionally, components marked “8/80” in the parts list on pages 14–15 have coverage of eight years or 80,000 miles, whichever occurs first. ...WARRANTY PARTS LIST

Air/Fuel Metering System

› Air/fuel ratio feedback control system

› Cold-start enrichment system

› Deceleration control system

› Electronic fuel injection system

— Air flow sensor

— Engine control module (8/80)

— Throttle body

— Other components

So, only the ECM has the 8/80 warranty. Even though the wire harness is causing the ECM to perform improperly, I don’t think they would cover the wire harness to 8/80, would they?

  1. I would elevate it to the next level with Scion Customer Care. Tell them you’re not satisfied with their offer and ask to speak to their manager or the next level up the chain. Keep at it until they make it right at no cost to you, or your patience wears out, whichever comes first.

  2. You could try to reset the codes, but there’s not much point. The driveability problem will continue until the root cause is fixed, and it will continue to throw code(s).

  3. I wouldn’t waste money with another mechanic until you get the harness replaced. It’s a known issue and it will cause problems until it’s fixed. Get the harness replaced, and hope that takes care of it. If not, then pursue further troubleshooting. But, another independent mechanic is not going to be able to diagnose/troubleshoot a bad wiring harness for you, and even if he could, why would you pay for that? You’ve already been told the harness is probably bad…by the people who made it.

“Basically what happened is they made a mistake in building the car, didn’t tell you about it, and when it failed…”

No, George, you are confusing recalls with TSBs.

Vehicle manufacturers DO notify vehicle owners of recalls on affected vehicles.
Vehicle owners are also notifed of extended warranties on specific components, such as the flawed transmissions on Honda Accords of the early 2000s.

TSBs are NOT sent to vehicle owners, and are only sent to dealerships and other mechanics so that they know how to rectify a problem IF it occurs. Some vehicles may experience the problem and others may not.

If the problem occurs during the period of warranty coverage, the TSB-related repair is gratis, naturally.
And, if the problem occurs after warranty expiration, then the owner is on the hook for the repair costs, naturally.

Consider a TSB to be an updated advisory on how to fix a particular problem IF it occurs.
It is NOT a recall, by any stretch of the imagination.

I could see them not taking care of you if a TSB applied to something that eventually breaks because of normal wear and tear but something that under normal circumstances outlasts the practical life of a car, like a harness…?
There’s a problem with something that should never have a problem, due to a bad design choice.

I guess it’s a leaner @TubaTwo. It depends on how much time you want to devote to the issue. And of course we haven’t heard Scion’s side of the issue either, so it’s hard to say for certain what’s fair to both sides. Splitting the cost 50/50 seems on the right track.

Probably what I’d say if I were in this situation is " ok, to quickly resolve the issue without a fuss for either side, I’ll pay for half of what Toyota charges the dealership for the harness part, and the dealership will pay the other half and install it with the labor fully at their expense.

Then the dealership isn’t getting the whole hit for the cost of the harness part, and they can use their employees who are already being paid to be there and likely have spare time in between doing the other jobs in the shop.

You might agree to sweeten the deal by agreeing to give them a week say with the car in the shop so they can fit the work in as shop time become available.

The only remaining question is will this new harness in fact fix the problem? Getting a second opinion from an inde who specializes in Toyotas, Lexus’s, and Scions might be prudent.

You might get it for free if you just briefly tell them the situation and not have them actually look at the car. Sometimes I do this in the normal course of aneighborhood walk and I’m pondering some car problem I’ve having. There’s a car repair place associated with a big retail store with dozens of bays and usually there is one of the mechanics outside taking a break, having a smoke, so I’ll chat him up a bit, tell a few jokes, maybe query him on something. Usually as long as I don’t press for particulars, but just general advice on the problem at hand, I can get some good info that way.