Check engine light?

Auto Zone result:
code P0421
Warm up catalyst system (RH) effeciency below threshold

Probable cause
1. Exhaust leak
2. Check other service codes first
3. Faulty catalytic converter

I bought this car at auction and found when I got home the check engine light was not working. Someone had removed the check engine lamp and of course when I put it in it was on.I scanned and found a few issues. All the sensor pids are displaying full voltage(5 volts). And also the pcm is reading 18 volt charging voltage. With a voltmeter I only have 11 volts at the battery.I am assuming it is the computer itself.I would like some more info on this issue before I replace the pcm

My car has been acting up. The airbag light would be flashing and my radio would turn on and off when it shut off it would not start again. I took the radio out and everything was working fine for a few days until the check engine light started flashing. I plugged in a code reader and it gave me the codes U3510 and C3F13 it has not shut off while it was driving since I took the radio out, but the battery has been dying when it is least convenient. The alternator maybe?

97 mazda protege. My check engine light came on again. I went to get and OBDII test and they gave me a code of P0420, saying it's either a O2 sensor or my catalytic converter. What is it more likely to be? If it's either one how much do they cost to get fix. Are the catalytic converters very expensive?

Hello. I have a 97 Mazda Protege, 156,263 miles. This morning my check engine light came on. I took it to an auto shop to get a diagnostic test. They told me that there computer connected to the engine's but it would not allow them to see the codes. He believes there to be a problem since the engine seems to be running rough, yet he said that could be a sign of a tune up. Also he just cut the light off and told me to drive and too see if it would come back on. I was just wondering should I follow what he said or go somewhere else and see if they can check the codes? Also, if the engine is running rough could this be a sign of expensive repairs to come?

Hello all.
I seem to be having problems with my little mazda protege.
For about a year now, the engine light will go on for a few days. Stay off for a few months, and then reappear suddenly. My dad had it checked out before, but was told it was just a faulty wire, because the car checked out fine, with no visible problems. Shortly after last summer, my overdrive will kick in all of a sudden (without me having to press a button) and the light will go on and off, all the while my car will kick in and out of overdrive at a rapid speed. We were told recently by a firestone tech that this could be a transmission problem. I am worried about how much this could cost, as this is an older car, and I don't plan to have it much longer. I have kept it in good condition, making sure it gets regular check ups, oil changes, ect. Within the past year it has gotten new belts, a transmission flush, and just within the past week a tune up that was badly needed.
I am a poor college kid, so I am not always able to cover the expenses as soon as I would like.
A newer problem as of late, is that when I try to start my car, the clutch appears "stuck". I have to let the car cool down first before I can shift the clutch into gear. At first I thought it was just the cold weather, but it has been warm these past couple of days, (70's) and my car still appears to have the same problem.
After I got my tuneup, it has slightly improved. The only time it appears to do this is early in the morning, and is fine through out the day, where as before the tuneup it would be anytime through out the day that I wanted to start my car.
If anyone could give me some insight into these problems, I would greatly appreciate it!

I just took my car in to be repaired. It was running rough and the Check Engine light started blinking. Had a standard tune up, replaced spark plugs and wires. The car is still running rough. The repair shop says I need a Complete Head Set $232.99 and a Magnaflux/Valve Grind $465.00. Are these prices high? The total of all the repairs needed are $2387.96 parts and labor, this includes other repairs as well.

I need some help. My car overheated when a friend of mine failed to put my radiator cap on correctly. I ended up losing all the fluid in my cooling system and let it cool before refilling it. It started to overheat a few more times and I had to bleed the air out of the radiator. Then the engine started misfiring occasionally when starting up and the temp gauge sometimes creeps up at long idles. Thought maybe there was still air in there and just keep trying to bleed the system. So I replaced the radiator cap, and got a thermostat and spark plugs/wires put on my car. And the temp gauge seemed like it was going up less frequently. But then 2 days ago the check engine light came on. And the temp gauge still sometimes creeps up on long idles. Also I can smell burning coolant. I fill up my coolant regularly but when I check my coolant level after driving heavily there are bubbles in the coolant. But once it cools down its low again. Its really frustrating. So I got the codes read and they are PO115 and PO420 help please!

I was told by a couple people that if it were the head gasket there would be white smoke coming out the tail pipe, which there is none, or coolant in my oil or vice versa, which there is none. What do those codes mean?