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Slow down! Don't panic! The codes are the result of a problem and may not pinpoint the real culprit. Use this site to get code definitions: http://www.actron.com/code_lookup.php
Just remember that the codes are generic and NOT precise.
First, the P0128 = Coolant Temp Below Thermostat Regulating Temp
I have never seen this one before! It says that the coolant temperature never got above normal in a few driving cycles. Does your dash temp gauge take a long time to get to "normal"? If so you probably need a new thermostat, but make sure you get an OEM. The generic thermostats, at half the price, tend to fail early and fail in the closed position - resulting in a cooked engine.
Second, the p0422 = Main Catalyst Below Threshold
Your cat is being over worked by a rich running engine. This is a good message! It means that your O2 sensors are still working properly. But, there is a problem. And that is probably due to the engine being driven a lot when cold. A "cold" engine signals the ECU to enrich the fuel supply, which then requires the CAT to get overworked, which is especially true when the secondary air pump stops running after about 2 minutes after start.
Did the above help? Take you car out and pay close attention the the temp display and note how long it takes to get to "normal" after a cold start. If it is not warm after 2-5 miles, get a new thermostat. If it is warm, then start thinking about the engine coolant temp sensor replacement.
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My name is Klaus and I am a Volvoholic.
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