Is the Check Engine Light Caused

by the Mass Air Flow Sensor?

Do Subcodes 0410 and 1411 indicate MAF Problems? Maybe. Probably not. Read on.


The CEL can mean a hundred things. Generally, it is a external warning set by the Engine Computer (DME) or Transmission Computer that something is wrong and the DME stores secondary “codes” that can be read by a mechanic to tell what is wrong.

You need to know the secondary codes to know what the cause might be. I use an Actron CP9135 ( (generally about $100 to buy it) to read and reset codes but you can also get the codes read at some auto parts stores (AutoZone is said to do it for free).

There are many other readers. They plug into a socket above the fuse/relay panel just above your left foot.

There is also software and a hardware adapter available that loads onto a Windows XP laptop. If you are buying for lots of cars, the Actron may be better fir simple testing to display the codes. Just for the Porsche, the Durametric is superior if you have a Windows XP portable with the USB connection as it can do so many more functions as well as triggering many chnages in the engine's coumpuer settings to help you diagnose a problem..

To find out what the codes mean on a Porsche, the best list is available for free on Or post the codes on an online forum and someone with the docs will interpret for you. You need to look at the DME Engine Codes for your Car Model (Boxster 986) DME 5.2 for years 1997-1999 and DME 7.2 for years 2000-2004.

There are multiple thick volumes written about how to diagnose a problem that your dealer has (The multi-hundred dollar multi-volume maintenance/repair manuals). Often the codes can have multiple causes. The dealer (and some independent mechanics) have multi-volume service manuals, PST2 code analyzers and additional diagnostic tools. The service manuals give the equivalent of flow charts to show how the mechanic should test to further isolate the real problem from amount the many possibilities. That the same code can be caused by several causes explains why, in forums, you can get people asserting that their fix is the right one for your codes when someone else is equally sure the codes point to a different cause/fix.

Be aware that there are codes that the Actron can't read that could be helpful in diagnosing a problem that a Porsche System Tester 2 (PST2) can.

Codes P0410 and P1411

Secondary Codes 0410 and 1411 are defined as "Secondary Air Injection Signal Implausible in cylinders 1-3 and 4-6 ". This points to the series of motors, valves and hoses that make up the secondary air injection system that is used to inject additional air on start up for emissions reasons. They are often incorrectly interpreted as being caused by the Mass Airflow Sensor (MAF). They can be, but most often are not.

What could it be?

Since the basic codes refer to the secondary air pump circulation system, the first question is do you hear the air pump come on when you are starting the car and it is a cold engine? Does it sound different from when the CEL wasn't coming on?

1 - Secondary air injection pump

2 - Air change-over valve

3 - Electric change-over valve

4 - Non-return valve

5 - To the cylinder heads

6 - Vacuum reservoir

7 - To the intake air system

The pump could have failed, the valves could have stuck, the lines could have clogged or developed kinks, etc. To diagnose, you probably need access to a PST2 tester, PIWIS or Durametric s/w and some good instructions like are in the Porsche Repair Manuals which show how to connect meters to specific probe points and what the readings should be and what they mean if they aren't right. This isn't something a person experienced in working on automobiles can't solve, but it is daunting for the beginner.

One thing you can do is on a cold morning when the car is cold, start the car and listen for the whine of the air injection pump. It should be on for 30-45 seconds and then shut off. If you can't hear it, tell your mechanic that.

You can trace at least the lines to see if there is an obvious loose line or an air leak. Specific diagnostic instructions are available here or here. For most of us, a trip to a dealer or to a mechanic who has a the right diagnostic computer and the other associated specialized Porsche tools is required. You can see from this parts diagram how many parts are involved.

From a posting by Loren on RennTech

I. ln menu "Drive links", trigger secondary air injection (AIR) pump.

1. Connect and switch on Porsche System Tester 2.

2. Select DME.

3. Call up "Drive links" menu.

4. Select AIR pump.

5. Activate AIR pump (audible function).

II. Check triggering of AIR pump.

1. Check fuse (Maxi Fuse) of AIR pump (on relay carrier2).

2. Remove relay of AIR pump (on relay carrier 2). Connect voltmeter to pin 3 and ground.

Display: battery voltage

Connect voltmeter to pin 2 (negative) and pin 7 (positive). Start engine (the DME relay must pick up).

Display: battery voltage

If 0 V is indicated, check wire from pin 2 to DME control module, pin 37, for continuity. Push relay back on.

3. Remove connector of AIR pump.

Connect voltmeter to pin 1 (positive) and pin 2 (negative). Trigger AIR pump with Porsche System Tester 2.

Display: battery voltage

III. Check electric change-over valve.

1. Remove two-pole connector of change-over valve.

2. Connect voltmeter to pin 1 (positive) and pin 2 (negative).

3. Trigger AIR pump with Porsche System Tester 2.

Display: battery voltage

4. Remove vacuum hose of change-over valve with the engine running. Check whether vacuum is present.

IV. Check air change-over valve and air supply lines.

1. Run engine briefly to produce vacuum.

2. Trigger AIR pump with Porsche System Tester 2.

3. Remove vacuum hose of air change-over valve. If vacuum is present at the air change-over valve, check

air supply from the AIR pump to the change-over valve to the air supply line to the cylinder heads.

Check function of air change-over valve.

Here is a video on diagnosing these CELs.

Try the MAF first?

The MAF sits inside the air intake just after the air cleaner, measures the air flow (mass and temperature) coming into the engine, and sends signals with the results to the engine computer so it can compute the correct amount of fuel to add to create the right fuel/air mixture.

It is safe to drive the car while these Subcodes are present. But not very efficient and the engine probably will run rough and lack power because the computer isn't getting a signal that it needs to do its job. Long term, you can damage the expensive catalytic converters by dumping unburned gas into them as the engine's computer tries to compensate for what is really wrong.

The MAF looks like this and is shaped so that it can only be inserted one way for the screw holes to line up. The sensors are the piece above that looks like half a paper clip and a shiny piece inside the tunnel just to the right of the paperclip in this picture.

If you want to know more about how it works, look at (but you don’t need to know just to work on it). I’ve added what the repair manual says at the end of this page for background reading so you can see what Porsche says about the MAF.

When the Engine Computer senses an individual signal or combination of signals that is not right, it sets the Check Engine Light (second from the left of the warning lights below your instruments) and the Secondary Codes so that a mechanic can see what is going wrong. These codes are present until they are cleared by an OBC II reader or until the battery is disconnected long enough to reset all the codes.

MAF failure is a common problem in all cars and most often occurs because enough air has passed over the MAF’s sensors to render one or both of them dirty. Less often, the MAF itself electronically fails. MAF problems are especially common in cars with aftermarket air filters especially ones that are oiled (too much).

To see if it is the MAF itself that is the problem, disconnect the MAF wiring harness and drive the car for a bit. Yes the car will drive without it because the ECU (Engine Control Unit) will go into a mode that doesn't use the MAF's input when it senses the MAF isn't sending any. If the problem changes for the better, either clean or replace the MAF. If it doesn't, you have another problem. Don't run the MAF-less car too long but a half hour won't hurt and is long enough for your diagnosis. To disconnect the MAF wiring harness, follow the first part of the "Cleaning" instructions below for raising the engine cover and remove the wires from the MAF without removing the MAF from the air intake. Should take no special tools and only about 10 minutes.

If it is the MAF that is the problem, before paying around $720 to the dealer to have them replace the MAF, there are 3 approaches you can take to lower the cost:

    1. Reset the codes. Since a single “not correct” signal will set the CEL, see if it ever comes back. Not recommended if the car isn’t running right

    2. Remove the existing MAF and clean it. You’ll need a specific Tamper Proof Torx bit to remove it and some electronics cleaner to clean it. Typically, you can clean the MAF once or twice and drive for 20k miles in between cleanings before having to replace the MAF. Total cost ~$20-35 for the initial cleaning, $0 for subsequent cleanings.

    3. If that doesn’t work, since you already are so proficient at removing and reinstalling the MAF because you did the cleaning, buy a MAF mail order for much less than the dealer will charge and install it yourself. Total cost ~$265-295. Any time you replace the MAF, you need to disconnect the battery for 5-10 minutes (have your radio code handy) so that the DME unlearns the settings from the old MAF and is forced, on startup, to learn the settings from the new one.

Number two is relatively easy, cheap, can be redone again for no cost (because you now have the cleaner and tool) the next time it is needed, and does no harm. And you can do number three if number one fails to cure the problem.

What Can a Dealer Do That You Aren’t Liable to Be Able To Do?

The dealer has access to the repair manual. The manual has tests the dealer can conduct using a multi-meter to see if the wiring coming to and from the MAF is bad or if there is some other computer problem.

The Do it Yourself MAF Guide to Cleaning and/or Replacement

These instructions are adapted from a posting on by ”Chris in NH” with my amplifications and pictures from several sources.

Required Legal Disclaimer

I am not a Porsche mechanic.

You use these instructions at your own risk. I accept no liability. If you can’t accept those terms, don’t use them.

If you find a problem with them, please advise me so I can either revise or withdraw them.

This assemblage is copyright by Michael W. Focke.

It may be linked to without permission but the contents may not be copied to or hosted on any other web site but my own.

I had this problem and followed these instructions. I had never been inside the engine compartment of my Boxster before I did it.

Cleaning did not fix my problem. It took me about an hour working by myself. I had one problem that caused me to revise my approach from what others had written. Next time, 20 minutes.

Before You Begin, Get the Right Parts

You need one not so common tool and a can of cleaner.

You'll need a size T-20 'security Torx' (also called ‘Tamper Proof’ Torx) bit or driver to remove the MAF from the air intake. When I went looking, this is what I found.

You can also buy individual (or a set of) Torx-drivers with a screwdriver-like handle.

You only need the T-20 Tamper Proof for this job but a set of the Tamper Proofs would be useful on other Porsche repairs such as the common ignition switch replacement.

The “Tamper-Proof Torx” looks like a screwdriver bit with 6-point bits (star shape). The tamper-proof aspect is that in the middle of the 6-point bit, there is a little hole in the bit so you need the special bit, not just the more common Torx. Make sure you get these, not the regular Torx bits that do not have the hole.

Tamper Proof Torx Bits

You also need a cleaner that will clean and leave no oil residue.

I found this one at my local auto parts store for ~$4.50. One can is enough for several cleanings and it does keep. It is a specific can labeled "MAF Sensor Cleaner" which is claimed by the PR gal at the manufacturer to be different than CRC's Electronic cleaner, and not just a relabeled electronic cleaner.

Remove the Engine Cover

Before you start work in the engine compartment, remove your belt and anything else that could scratch the paint as you lean over the car. Use old towels to protect the fender’s finish on both sides just to be safe as you’ll be leaning over the fenders to get at things.

The engine compartment cover removal procedure is covered in the owner's manual (pages 179-182 in mine) with pictures, is a one-person job, and is pretty easy. Just take your time. It involves parking the top part way up, unhooking it, strapping it up out of the way ( never found the strap and mine stayed up without it), removing the cubby box behind the seats, the sound deadening upholstery and removing the engine cover. You need no tools for this. You do need a place to set 3 car-wide items (good time to get the vacuum cleaner out and clean them).

Locate and Remove the MAF

Once the engine cover is off, locate the MAF (see picture below). It is tucked under the lip of the engine cover hatch just behind the square box where the air filter is located on the left side of the car (while you are in there, might as well spread those clips on the flat cover and look at the condition of the filter).

The flat piece on top with the stop-sign like sticker is the air cleaner cover, just to its left (or rear) you see the wires connecting the MAF to the DME. Remove the wires and socket that connect to the MAF by pinching the long sides of the top piece of the plug. Then wiggle the top socket loose from the bottom half. Pull on the plastic of the socket itself, not the wires. The trick is to separate the outboard clip that holds it on, then it wiggles lose easily. That didn’t work for me. I removed the MAF itself (next step) and unloosened the socket where I could see it. Don’t touch the wires on the MAF, touching the black plastic is OK.

Remove the MAF by loosening the two “screws” using your T-20 Tamper Proof Torx bit in the end of a screwdriver handle or long socket extension. Don’t lose them. It’s a two handed job to unscrew and hold them as they come out unless your handle was magnetized. They go back on hand tight (3-4 Nm, 2-3 ftlb) as they screw into plastic.

Top view of the MAF looking from above showing the socket the wiring harness plugs into. Don’t let the MAF sensors touch anything as you lift it from its socket, hold it by the plastic.

Inspect It

Once you have removed it, inspect it. If it is covered with oil, suspect you have another problem (dirty K&N?) which is causing the contamination. Solve that failure first as it will affect other (and more expensive to fix) sensors downstream of the MAF eventually if not now. If it has just accumulated some dry stuff from lots of miles worth of air passing over it, then try the “clean it” approach.

Clean It

Clean your MAF to see if that helps before buying a new one ($260 to $440!). Take out the MAF, get a can of electrical contact cleaner (sample pictures above) and spray it into the hole in the MAF with the little wire inside and onto the portion that looks like a paper clip (see picture below). Let the contact cleaner drip off the MAF so that any dirt, etc is washed away. Don't try to touch the sensing surfaces with anything. I shake the MAF vigorously while holding it by the part that shows the green washer in the picture. You can do this a few times just to make sure.

Reinstall It, Replace the Engine Cover, Connect the Top

Let it dry, then reinstall it and reconnect it. Reverse the steps to replace and secure the engine compartment cover and reattach the top.

Clear the CEL

You now clear the CEL using your code reader (see the code reader’s instructions, it is usually just a push of a button or two with the key on, engine off) or by disconnecting the negative terminal of the battery for more than 20 seconds, but less than 50 seconds on a pre '03. If you do the battery disconnect on a pre '03, you will clear the CEL and won't need to re-code the radio. The radio loses it's memory after 50 seconds w/o power, but the car's memory needs to be disconnected more than 20 seconds to clear the error codes.

Drive for a While to Test It

Drive for a while, and see if your CEL comes on again with the same codes.

1. If it doesn’t, you won.

2. If the CEL comes bask on and you have the same codes, then you can have one of two problems.

a. Either a bad MAF that cleaning won't fix

b. or a good MAF and a problem that is causing the code that seemingly points to the MAF.

My experience was this latter. If it is the first (2a above), you buy a new MAF mail order at a discount and use the experience you gained by cleaning the old one to replace it in half the time. That is the first thing the dealer would have done and they would have charged you full price for the part plus labor (around $720 total!). But how do you know it is the MAF itself? For that you go to a dealer or an independent Porsche mechanic who can diagnose the wiring or DME failure possibilities by using the procedures in the Repair Manual. If I thought you had the Repair Manual and were that good, I’d be betting you wouldn’t have been looking at these simplified instructions <grin>.

Good luck, see you in the twisties.

If You Have to Buy a replacement MAF

Depending on the model year, there are two different MAFs. One is for non-E-Gas engines (Model Years 1997-1999), and the other is for E-Gas engines (MY 2000-2004). And the E-Gas version has had two revisions.

Take out your old MAF and check the part number on the MAF to match it with the Bosch part number to see what you need. This is what the non-E-Gas version looks like.

With thanks to Wayne at Pelican parts for some of the above info

The ones that came with the 986 606 124 00 MAF require a dealer reflash of the ECU when the 124 part is replaced by the 125 part.

The 986 606 125 00 was discontinued and replaced by the 986 606 125 01. The Boxsters that normally came with the 125 00 MAF did not require an ECU reflash if a 125 01 was used.

All E-Throttle Boxsters with VINS greater than these listed had the new style 125 MAF and program :

Boxster 98 6YS 620415

Boxster 98 0YU 625100

BoxsterS 98 0YS 660258

BoxsterS 98 3YU 662414

as described in the Boxster TSB 2445 (Air Flow Sensor) dated Apr 6, 2001

The car should drive as far as the dealers with the new part in it without harm and the total labor to load the new firmware into the DME should be about a half hour.

Beware MAFs sold on eBay. They are often the old bad part someone replaced.

You can buy using either the Bosch or Porsche part #, whatever is cheapest and most available.

You must only use an E-Gas part in an E-Gas car.

After you replace a MAF, you will also need to disconnect the battery for 5 or 10 minutes and see if that improves things. This will force the ECU to learn the new settings coming from the new MAF. After a few trips, things will be back to normal ans the ECU will sort out the normal from the abnormal.

Don’t pay list if you buy one, shop at your local auto parts store and online.

MAFs are often advertised on eBay. But most of those ads are technically incorrect and don’t differentiate between the E-Gas part and the non E-Gas part. Buy only if they specify a clear part number, either Porsche or Bosch. Many are unloading the MAF they replaced so beware.

If you have a correction or suggested improvement to these instructions, feel free to contact mike.focke at his address.

From the Boxster Repair Manual

10. Hot film mass air flow sensor

A new hot film mass air flow sensor with the designation HFM 5 is used on the Boxster. Its housing shape permits installation in one direction only. It is fastened with M 5 Torx screws. As with the previous mass air flow sensors, the manufacturer performs laser calibration on the new HFM 5 in a so-called "master tube". In other words, a corresponding air mass produces an exactly defined voltage signal.

The hot film mass air flow sensor is fitted in the air cleaner housing at the outlet of the air cleaner. The operating voltage range is 9 -7 Volt, and the output voltage of the mass air flow sensor (voltage to the DME control module) lies between O and 5 Volt. The actual measuring element is supplied with a controlled voltage of 5 Volt from the control module in addition to the voltage supplied by the vehicle electrical system to the mass air flow sensor. This prevents fluctuations in the vehicle voltage, e.g. when loads are switched on, from influencing the measuring process.

Intake air temperature sensor

The intake air temperature sensor is installed in the mass air flow sensor housing and is thus located in the intake air flow. It is supplied with voltage by the DME control module via terminal 43, and is connected together with the HFM 5 on the ground side. The intake air temperature sensor functions according to the NTC principle. The DME control module uses the signal from the intake air temperature sensor to calculate the substitute load signal if the mass air flow sensor fails. The load calculated by the control module, which depends on the throttle potentiometer, is corrected by the IATS signal. A negative correction is applied to the substitute load signal at high air temperatures.

At the same time, the decreasing air density is compensated. Furthermore, the risk of knocking increases with increasing intake air temperature. The ignition timing is therefore retarded at a high engine temperature (> 90 °C) and high intake air temperature (> 30 °C).

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