How do I know which O2 Sensor to replace on 2004 Dodge Ram - Error code P0134?

the code should tell you which bank and sensor to change ex bank 1 #2 which is right side the second one

only the dealer has the diagnostic equipment to know.

If that's the problem code, it's telling you. P0134 O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1) Bank 1, driver's side, sensor 1, fore of the cat. But it isn't saying the O² sensor is bad, it's saying there is no activity detected. It could be bad, but it could just be the plug isn't on tight, so check that first.

P0134: 02 Sensor Circuit No Activity Detected (Bank I Sensor 1) Bank one is the side with Number one cylinder(left) Sensor 1 is the sensor before the catalytic converter. Check the wiring to the sensor carefully for shorts or that is not disconnected at the plug. These are rare, but possible. Some code readers will give the description of the code on the screen, most don't, that is why you need the book. If you don't have a book, type the code in Google.

For a code P0134 just replace the oxygen sensor on the driver side front of the catalytic converter and done with it.The scanner does not tell which one,only interpretation from the code number.In your case it is bank 1 sensor 1.

It's referring to the oxygen sensor that is on the same side as cylinder #1 and forward of the catalytic converter. Your sensor may be disconnected somehow or simply no longer good.

Before I'd invest into parts like o2 sensors for sure I'd want to know if it's not a error code that is related to a totally different problem. Example you could get a error code or comp code that indicates a upstream o2 sensor is faulty but in actual fact it's something else related to improper gas and air mixture or a bad spark-plug or plug wire etc.So I'd want to be sure that the plugs , wires and connections on the ignition module are all good , plus check vac lines , vac hoses , air filter, plus dirt or moister in the fuel system could cause such codes too. Another example is you get a downstream sensor code this could mean that the cat converter is acting up or faulty so be careful when dealing with o2 codes bec they only mean that the comp has picked up or received an odd or unusual reading. Another example is you get two upstream codes and one downstream code that would tell you more then likely the problem is before the sensors. Hope that helps and best of luck.By the way any good shop should have a good enough scanner that they can hook up to your vehicle and then pin point exactly what is giving the comp the error code. If I were you I'd treat the fuel system with something like Lucas or STP fuel treatment and then one you use up a few tanks of gas change the fuel filter and see if the code goes away.

Usually O2 sensors are good for about 100,000 miles before they need to be replaced. A PO134 is a generic code, all generic codes start with a PO, an actual hard fault would start with a P1, it is just indicating that the O2 sensors could be part of the problem but aren't necessarily. Anytime you replace the 02 sensors you replace them as a pair. The two upstream sensors are the two that give feedback to your OBDII or are computer controlled. The two downstream sensors are not computer controlled but they do supply the computer with info. concerning the exhaust, after it passes through the converter. Places like auto zone have ok software,but you really need to get it scanned on a scanner such as the dealers or a big garage that works on all makes and models to truly find out what or where your problem is. Then you'll know what the problem is and can go from there, knowing you are fixing the correct problem.