Have two codes on 1999 chevy blazer

P0101....Mass or Volume Air Flow Circuit Range/Performance Problem
P0121 - Throttle Position Sensor/Switch A Circuit Range/Performance Problem.
P0420 - Catalyst System Low Efficiency
there is criteria that enable trans shift
solve codes problems then transmission will shift normaly

the code is for
mass or volume air flow circuit range/performance problem

P0101 ISUZU - Mass Air Flow Circuit Performancehttp://engine-codes.com/p0101_isuzu.htmlForum CodePossible causes- Dirty mass air flow sensor
- Dirty mass air filter
- Mass air flow sensor harness is open or shorted
- Mass air flow sensor electrical circuit poor connection
- Intake air leaks
- Faulty mass air flow sensor
Tech notes Before replacing the mass air flow sensor, try replacing the air filter and cleaning the air flow sensor with low compress air or mass air flow sensor cleaner. Reset code and drive vehicle. If the code comes back, it may be necessary to replaced the mass air flow sensor

P0101: MAF or VAF A Circuit Range/Perf

- Dirty mass air flow sensor
- Dirty mass air filter
- Mass air flow sensor harness is open or shorted
- Mass air flow sensor electrical circuit poor connection
- Intake air leaks
- Faulty mass air flow sensor

Before replacing the mass air flow sensor, try replacing the air filter and cleaning the air flow sensor with low compress air or mass air flow sensor cleaner. Reset code and drive vehicle. If the code comes back, it may be necessary to replaced the mass air flow sensor.

P0101 is the Mass Air Flow Sensor error,
http://www.obd-codes.com/p0101


P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature

Ok, it's not the transmission.
P0101 maf sensor ( mass air flow) sensor. Change the sensor, it is located in the air intake hose that runs from the air filter housing to the throttle plate/ throttle body. Disconnect the wire from it and loosen clamps ( if equipped) and pull hose from it.
P0128 thermostat is below temperature specs, change to a 190 or 195 degree thermostat. auto parts store should be able to tell you which one you need.
P0155 the heater circuit in the oxygen sensor is bad, need new one. That is on bank 2 sensor #1. If it is a V6, looking at the engine, it would be on passenger side, screwed into the exhaust pipe near the exhaust manfold.

404 is exhaust gas recirculation circuit, and 405 is exhaust gas recirculation sensor circuit low. EGR sensor or ground?

with the p0101 make sure you have a clean air filter. it can be bad spark plugs and or wires, or a leak in the air intake system

Hello mark...according to the manual for Volkswagen Engine and Transmission Codes...

P0101 Mass or volume air flow circuit performance problem

P3131 Exhaust Gas Recirculation (EGR) System Control Limit Exceeded

Dirt and carbon build up will cause this in some cases. You might try removing and cleaning the MAF sensor with an electrical contact cleaner first. You will still need to clear the error codes with VAG-COM and see if they return.

Good luck...i hope this helps.

P0404 Exhaust Gas Recirculation Control Circuit Range/Performance
P0405 Exhaust Gas Recirculation Sensor “A” Circuit Low


It sounds like you have a failure of the EGR valve.