Had car scanned codes PO601 came up 1x code Po420 came up twice. sum say the ECM going out

code p 0601 refers to engine control module ( ECM) memory check sum error ===causes--- ECM
to correctly reset an ECM use a scan tool for the job
removing the battery can corrupt the CPU program of the ecm and while if can work in some instances there are many cases where other problems are created by that method
Try substituting a know good ECM if the reset fails

even a 01 has a diagnostic port on the ecm you'll need to find an older model scan tool and retrieve fault codes to learn more , also ck fuses both under hood and under dash there might be one or two bad

check crank shaft sensor and cam shaft sensor these wont always bring up fault codes check them with a oscilloscope

The computer or ECM constantly tests operation of all sensors and components. When any of the sensor signals is missing or out of normal range, the ECM sets a fault and illuminates the "Check Engine" or "Service Engine Soon" light also called MIL (Malfunction Indication Light) storing the corresponding Diagnostic Trouble Code (DTC) in the ECM memory.

The same happens if a mechanical component of controlled system fails. For example, mechanical problem inside the transmission also can turn the "check engine" light on. Even not properly closed gas cap will cause the "check engine" light to come on - the ECM constantly checks if the gas tank is sealed properly.

To sum up, when the "Check Engine" or "Service Engine Soon" light comes on and stays on, there is a problem with your vehicle. This could be a problem with the engine, transmission, or some emission-related component or system.

The stored trouble code can be retrieved with the special scan tool by the technician. The code itself does not tell exactly which part to replace, it only gives a direction where to look for - the technician has to perform certain tests specific for each code to find the exact cause of the problem.

Scanning for knowed exactly what fault code you have there.

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you may have a bad converter, its not cleaning the exhaust, but on the other hand a bad rear o2 sensor can also cause this problem,there is a wat to test but you would need a scan tool or scope,replace the other sensor, if light returns then replace the converter, no money lost, if you were to replace the converter the o2 sensors should also be replaced. you have 165000 miles it would be crazy not to replace sensor and install new cat, so basically your just doing it in 2 steps and may get lucky and not need a cat. good luck.

In almost all cases, a P0420 code indicates a problem with 1 or more O2 sensors. They send incorrect emissions information back to the ECM and trigger the Check Engine Light. If the Catalytic Converter is fine (no problems with the engine hesitating or getting a lot of heat from under the car) then it's most likely the O2's.

Check engine light with no codes usually means a PCM reset is happening. EBP shorting, ICP shorting, aftermarket "performance chip". PIDS need to be monitored to eliminate sensors. IDMs (Injector Driver Modules) can also cause this. IDM's are separate from the PCM/ECM (engine computer).

If the code has cleared on its own then you need to disconnect the battery and re-connect it. This will clear the codes out of the memory. If you don't want to do this you can go to an auto parts strore and have them hook the little computer up to your car and they can clear out the code as well.

Get the engine control system scanned, that is the first step here.

most of the time its the sensor that cause this,id try replacing the sensor on it,that usually fixes that code,but you have to get the code cleared off with a scanner ,and then re-scan it to make sure it doesn't come up again,good luck with it.