Having problems with your 2005 Pontiac Grand Prix ?

Check engine light on got a diognostic and code P0128, P0420, and P0455 popped up trying to figure out what these codes mean and what I need to fix on my car

Posted / edited by AnonymousUser on : 12-11-2018

Answers :

P0128 ECT Sensor Below Thermostat Regulating Temperature

P0420 Catalyst System Bank 1 Low Efficiency

P0455 EVAP System Large Leak (0.080") Detected

For the 'P0128' your engine isn't getting up to operating temerature. This could be because of a low coolant level or your thermostat is stuck open. For 'P0420', this indicates your catalyst isn't working as well as it should. If you have a four cylinder, this will be the first cat in the system, if you have a V6, then it will be the one on the driver side. Since this code can also indicate a clogged catalyst, you should get this checked at an exhaust shop. They can do a back pressure test to see if it is clogged. For the 'P0455', this indicates you have a fuel leak from the pressure system in the fuel tank. The EVAP takes fuel from the tank that builds up pressure and stores it in a canister until you start the engine. Then it shunts this fuel into the engine to be burned.
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