Mazda 626- Exhaust leak in rear manifold

My Mazda 626 is in service for an engine warning light and my mechanic says that they will need to plug an exhaust leak in the rear manifold - est. cost $660 mostly labor. And he’s not sure that will solve the issue - a new cat converter may or may not be needed. My questions are

(1) If I do not do this work, what will happen?

(2) Does the price sound right? (About 4-5 hours labor)

What Model-Year And How Is This “Mechanic” Going To “Plug” A Leaking Exhaust Manifold For $660 ?

How many miles on it ? Do you have a receipt (repair order) that tells what DTCs (diagnostic trouble codes) were discovered ? We’d like to know what code(s) go/goes with the “Check Engine” light.


It’s a 1999 626 ES with 175K miles.
The DTCs were P0122, P0420.
My bad, they would like to replace (not repair) a leaky exhaust manifold.
That will then allow them to tell whether the problem is just that, or if the catalytic converter also has to be replaced.
The part cost is about $250 and labor would be another $300.

Bump - Up To The Top Of The List.
Thanks For The Good Info. I’ve Got To Leave Right Now For Several Hours, But With This Good Information, I’m Pretty Sure You’ll Receive Some Advice You Can Use. I’ll Be Back.


I’m Back. Where’d All The Techs Go ? I’m Not A Tech, But Let’s Get This Discussion Rolling.
P0122 = TPS (Throttle Position Sensor/Switch) A Circuit Low Input
P0420 = Catalyst System Efficiency Below Threshold (Bank 1)

Has there been any discussion about the TPS (throttle position sensor) ? I know that this can cause both of the codes that you indicated. It, or its circuit is a candidate.

PO420 is one of the most common DTCs found when a “Check Engine” light comes on. Many problems can set it off. Catalytic converters are too often blamed for a code PO420 and too often replaced when it isn’t necessary. I’m not saying that the converter isn’t bad, but it very well may be just fine.

Do you know what is wrong with the manifold (leaking) ? Cracked ? Rusted through ? Other ?
Exhaust leaks can cause fault codes to appear, but I’m surprised that an oxygen sensor wouldn’t be setting a code because of the leak.

This is a V-6, right ?


Any Problems With The Way It’s Running ? Rough / Poor Idle ? Other ? Can You Hear An Exhaust Leak Under Any Conditions ?


Short answer is no. When this was diagnosed, there was another repair done to replace the fuel throttle sensor, which had caused issues with idling and running rough. Now that it is done, the car runs smoothly.

Just noticed your previous response. So it was the TPS and interesting that it could cause both codes. Thing is, when they returned the vehicle to me, the engine light remained on. Should I ask them to turn it off and then monitor if it comes on again?

Yes, I’m Surprised They Didn’t Turn It Off For You. Monitoring Is A Good Idea. If The Problems Are Fixed However, The “Check Engine” Light Will Turn Itself Off After A While.

Don’t drive if the “Check Engine” light is flashing, only if it is steady. Most “chain” type auto parts stores like Auto Zone, Advance, etcetera will have a counterman come out to your car in the parking lot and read your fault codes and turn your light off for you, free of charge. Keep a record of any codes they give you and see how long it takes for the light to come back.

Again, do you know why they say the manifold needs replacing ?

So it was the TPS and interesting that it could cause both codes.” Sometimes a problem with one part / circuit / system can cause multiple codes to be set and retrieved. They are clues as to what is happening, but don’t necessarily pinpoint the cause.


The check engine light is stable and not flashing.
They say the manifold needs replacing because it is leaky. This conclusion is based upon the diagnosis they conducted - of course I can’t be sure if the manifold was physically inspected or if it is simply based upon the diagnosis code.
The auto shop is a well-established one with a good reputation, but I can’t seem to get away from major work every time I come in - hence my hesitation to go ahead with this one. For now, the car is out of the shop and running well.

For Around 50 Bucks You Can Buy A Basic Code Reader, Like The Actron Pocket Scan, Read OBD2 Codes And Turn Off The Light. I’ve Got One. Works Great. Sears And Auto Parts Stores Sell Them.

They come with a list of codes with brief descriptions of what system they are asscocited with. Also, there are sites with more information, useful in diagnosing.

At almost 12 years old and a 175K miles on this Mazda, I’ll bet that you don’t want to see how much money you can “invest” in it. The problem with the “Check Engine” light on all the time is that you can’t tell if something else is going on that is a new problem.


CSA, thanks for the useful advice! I appreciate the time you’ve spent responding to my questions.