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Lamp, ASE Certified Technician
Category: Car
Satisfied Customers: 200
Experience:  Ase certified Electronics, Brakes, Steering and Suspension
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2002 Mazda Mpv: harness..misfire again, diagnostic, number 5 pack

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2002 Mazda Mpv diagnostic, multiple misfire, changed harness and plugs, and rear O sensor, misfire again, diagnostic, number 5 pack replaced, engine light back on one day later, diagnostic number 2 sensor bad, and that's where it stands. What I don't understand is why didn't they catch these others initially or did they mis-diagnose from the beginning?

Hello thank you for using JA let me see if I can help.


The majority of the time for a misfire to happen it could be a number of things, a failed coil, wire or spark plug. A compression issue with the engine which is caused by internal engine issue. A failure or issue with the injector for that cylinder. An 02 sensor will not cause a misfire. It is rare that a vehicle will have multiple failures like this unless the vehicle has been operated for a long time with the issue. By the sounds of it they misdiagnosed the issue.

Customer: replied 8 years ago.

Thank you for your feedback. The mechanic is not saying that the 02 sensor will cause another misfire they are only saying that the diagnostic for the engine light is a failing 02 sensor. However this is after all of the other work has been done. In other words one thing seems to be causing another to fail, but that doesn't make sense to me. He says this second sensor is easy to replace but as a part is about $120.

Customer: replied 8 years ago.

If you say an o2 sensor will not cause a mis-fire and they say the diagnostic says its an o2 sensor, then basically you are saying that the diagnostic is wrong, correct? So are saying that engine light diagnostics can be mis-read?

That is correct the only thing an oxygen sensor does is tell the computer how rich or lean the mixture of fuel is. A miss fire is caused by a cylinder not firing, in order for the sensor to cause a cylinder not to fire it would have to stop all fuel to the cylinder. The miss fire will be due to the ignition system or engine troubles. It would have to be a dead miss at all times like a dead injector for the fuel system to cause the miss fire. What I am saying is that it is possible the oxygen sensor is bad but this is not the cause of the miss fire.
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