Po 420 ?

SOURCE: check engine light on

P0700 - Transmission Control System Malfunction, this is a transmission or PCM issue and needs further diagnosis with other test gear.

The P1684 code simply means that the battery has been disconneted within the last 50 engine starts.

SOURCE: PO 1665 code 1998 buick rivera

EVAP is for Evaporative emissions control system, so no this is not EGR, that is Exhaust Gas Recirculation system, as far as the P1665 goes it is related to the other trouble code P0440, u will need to replace the EVAP system Purge flow control solenoid. This should correct both problems after u replace the part disconnect the battery for 5 min's to reset system.

SOURCE: engine misses at 35 mph code po 304 coil pack plug wire replaced

Information courtesy of http://obd-codes.com

A code P0304 may mean that one or more of the following has happened:

• Faulty spark plug or wire
• Faulty coil (pack)
• Faulty oxygen sensor (s)
• Faulty fuel injector
• Burned exhaust valve
• Faulty catalytic converter(s)
• Running out of fuel
• Poor compression
• Defective computer

Possible Solutions If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.
If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. I would suggest spark plugs, spark plug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. I've also heard in other cases the problems were faulty fuel injectors.

Hope this helps with your problem. Best of luck.
Greg

SOURCE: 2004 chevy aveo that the

P0128 - the thermostat may be stuck open or has anyone put a colder thermostat in the car,because once it starts to get cold it will throw a SES with a colder then stock thermostat. Replace the Thermostat should fix this problem.

PO700 is a code telling you there are codes in the TCM of some late model cars where the Transmission control module has been removed from the PCM the vehicles main computer , and basically it happens when the TCM has a issue within itself or the transmission that sets a code and it sends a request for the PCM to illuminate the SES or CHECK engine light. To get at the TCM codes requires in most cases the most up to date scanner software purchased after the cars model year and as of yet is still a little iffy. Standard OBD11 scanners will generally not be able to see these codes.

P1781 is set during engine start up when the ECM & TCM do not communicate properly during initial power up. It will only illuminate the service light if the condition occurs in 2 consecutive start cycles, but the DTC will be stored in the failure records after the first cycle.

Replace the Thermostat and go to a transmission shop that can read the DTC codes with a scanner and reset the ECM for clear the codes. Most Transmission shop will do that free of charge, if not turn the Ignition key's to the on position and and pull the ECM fuse out for 30 seconds and then place it back in. Turn the ignition keys to the off position for 10 seconds and then start the car, the engine may stall but let it. Just start the engine again, the ECM is just relearning the engine and go for a test drive. This will clear all the DTC history in the ECM like the day it cam off the assembly line. Good luck and keep me posted, be glad to answer ay more question.

SOURCE: My 2000 Ford Ranger keeps showing codes PO 171 and

These codes mean that the oxygen sensor is reading too "Lean" on both the left and right cylinder banks and the engine control system can't compensate any further to solve the problem. You may have a dirty or failing Mass Airflow Sensor that is miscalcuating the amount of airflow the engine is taking in which in turn can cause both of these codes to set. If the sensor is reporting less air than the engine is actually taking in then the engine computer will add only the amount of fuel it should based on what it was told by the sensor which will cause both cylinder banks to run "lean". There could be something else going on such as having two bad oxygen sensors [very rare] but I do see these two codes together quite often and usually its the sensor that is causing it. Hope this helps a bit!