EGR Valve Test

Last updated: April 12, 2000

Date: Mon, 14 Dec 1998 23:49:43 -0500
From: Patrick Gaines

>I have an error code 16 which is an "EGR switch open or short circuit".
>Can anyone tell me where to start looking to correct this problem?

I had the same code for quite some time. First, if your car is less than 5 years old and has less than 50k miles you may be able to get it checked, repaired, or replaced under the Mazda original emissions warranty (be wary of the dealerships, however). According to the warranty info that came with my car, the EGR system [including "EGR function control valve (EGR control valve) and associated parts (EGR valve, EGR valve control solenoid)"] is included.

Many other systems are covered such as O2 sensor, MAP sensor, fuel injectors, idle air control valve, air valve, decel. controls, purge valve and solenoid, fuel filler cap, PCV valve, air pump, CATs including pipes, and other miscellaneous hoses, gaskets, clamps, etc.

If you live in California, you have 7 years or 70k miles with a much more extensive list of components covered (including turbos, fuel pump, intake manifold, throttle body, PCM, inter cooler, and others!). READ your warranty info.

Warning: some of the stipulations for warranty coverage are vague and may require that you can not pass a government mandated emissions test and that you face penalty if you do not pass the test. Before you go into a dealership, make sure that you read the warranty stipulations word for word and are prepared with an argument for why you should be covered.

Anyway, back to your question. I recently investigated my EGR valve. First, I performed the actuator vacuum test outlined in the manual. My valve would not hold vacuum, which made me suspect that the EGR valve actuator was bad (turned out it would not hold vacuum and the switch did not work).

This check engine code is simply to verify that when the computer tells the EGR valve to actuate, that it actually actuates. The switch is connected to the end of the valve and after a certain amount of travel, closes the switch to tell the computer, yes I actuated. If the computer tells it to actuate and does not get the closed signal from the switch, it will output code 16 and illuminate the CE light. This seems to be a very common problem.

This test is performed with a vacuum tester, if you don't have one, go to any auto parts store and buy one ($25-$35). This is an essential testing device for many RX-7 components. This is what to do:

  1. Locate the EGR valve on the right side of the intake manifold. You may have to remove various parts to get to valve and remove valve and its heat shield (depending on test and accessibility).

  2. Remove hose attached to actuator and connect the vacuum pump to the actuator.

  3. Apply vacuum of 4.5 inHg max. Will it hold vacuum? If not, you either have a bad actuator or the sensor switch o-ring is not sealing properly.

  4. If it will hold vacuum, the switch could be bad (this was also my problem).

  5. Valve itself could be the problem. Remove valve from manifold.

That's about it for the EGR valve side of troubleshooting code #16. Of course, the harness back to the computer could also cause a problem, but I will assume based on the history of this component that that is not your problem.

Beware, no part of the valve is serviceable by Mazda (i.e. o-rings, switch, internal components) so if you can't fix it you will have to get them to cover it under the above warranty or shell out the $100+ to replace the valve + $4 for the gasket.

I am sure you will hear many people on the list tell you just either to forget about it (live with it) or remove it and install a blocking plate as valve malfunction can seriously affect the performance of your car (especially at low idle). However, I am not so easy to give up on this as it does serve to reduce combustion temperature and reduce the amount of NOx gases from the car.


Date: Thu, 21 Jan 1999 10:48:46 -0600
From: "Westbrook, Chuck"

The ECU monitors only the function of the solenoid that opens the EGR valve. It only functions under light loads above idle. Just pull off the vacuum hose from the EGR valve and plug it to disable it.

I left all my hoses on the outside so that all looks normal, but pulled and plug the hoses underneath the intake runners that are for the EGR operation. This way everything looks normal, but the EGR valve is inoperative.

While installing my new engine, that's when I could see the carbon buildup caused by the EGR inside the intake manifold. Disabling it will not give you any more power, but will reduce exhaust residue buildup in the engine.

From: Rob Robinette

How the EGR System Works

If you care here's how the exhaust gas recirculation (EGR) system works. A few years ago scientists discovered they could reduce the formation of nitrogen oxides (NOx) during combustion by keeping combustion temperatures below about 2500 degrees F. They did this by injecting an inert (non burning) gas into the air/fuel mixture of the engine. The inert gas helps cool the combustion event to below the threshold where NOx are formed. It turned out that exhaust gas works well as an inert gas.

The EGR valve allows a metered amount of exhaust to enter the intake of the RX-7's engine. The EGR valve uses vacuum and an electrical signal to open the valve and inject the exhaust. The valve is closed with no vacuum present (yes, if you remove the vacuum line you will disable the EGR). The chart on page F-125 of the Mazda 3rd gen Workshop Manual shows that the EGR valve only opens under relatively light loads between 1050 and 3850 RPM. It is closed at idle, deceleration, RPM above 3850, and heavy load.

So it seems that there would be little benefit in disabling the system. The emission book, "Understanding Automotive Emissions Control," (available at Barns and Noble) states that an engine may need it's timing retarded and/or the air/fuel mixture richened to prevent detonation. I've heard from more than one list member that has disabled the valve with no change in engine operation.

The site can be found at:


Date: Sat, 3 Apr 1999 21:36:51 -0500
From: "Rob Robinette" (

All 3rd gen RX-7's have EGR (Exhaust Gas Recirculation not return) valves, but the California models have an additional electrical control on the valve-see the Workshop Manual. The PCV (Positive Crankcase Ventilation) valve is a one-way valve that is between the oil filler neck and the extension manifold on 93 and 94 cars. It allows vacuum in the intake to suck blow-by gasses out of the crankcase and prevent them from venting to the atmosphere. When the intake is pressurized (boost) the PCV valve prevents pressurizing the crankcase. The 95 cars have only one vacuum line connected to the oil filler neck-it goes to the air filter side of the turbos (93 and 94 cars have this line too). This vacuum line is always under vacuum, even when the turbos are generating boost, so a PCV valve isn't needed. It's very easy to remove the short vacuum line and PCV valve on 93 and 94 cars and plug the openings on the neck and manifold.

You don't need a blocking plate to disable the EGR on 3rd gens, just pinch or plug the vacuum line that goes to it. You won't notice a performance improvement though. The 3rd gens' EGR is only used under light load and certain RPM.


Date: Mon, 10 Apr 2000 11:31:28 -0500
From: "Westbrook, Chuck E." (

> I performed the diagnostic for when the Check Engine light comes on and I
> got back error code 16.  Its my understanding that this is the EGR valve
> from the California spec cars.  I live in NC and so does the car (its whole
> life).  Is there a way to see if for some wierd reason I have a California
> car?

The EGR will have an electrical connector on it if the car is a CA one. The non-CA cars don't have this. Also check the ECU number. My 92 has the N3A1R rebuilt N3A1 ECU. A friends CA has the N3C1A1 ECU. Later non CAs have the N3A2 ECUs.

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