Question

2000 GMC Savanna Van 1500 5.7L with engine codes P0171, P0300, P0420, and P1870, how do I fix those codes?

Answer 1

P0171 Fuel system lean bank 1

P0300  Random misfire,

P0420 Catalyst below threshold

P1870 Transmission component slipping (4x4 switching circuit)

Fuel system lean bank 1,where the number 1 cylider is located, that means standind in front of the vehicle the closest valve cover to the front is bank 1,you need to look for a vacuum leak,if you dont find any look at the condition of the sparkplug, at the same time we shall address p0300 random misfire,random means more than 2 cylinder,P0420 is the result of the lean running condition, so concentrate on the lean misfire, A EGR (exhaust gas recirculation) pintle being slightly open do to debris can cause random misfire and yes it can affect the nearest bank which happens to be bank 2. So the EGR needs to be inspected.and another is sparkplug wires shorting to ground randomly,I belive it will be in your best interest to start with the EGR ,if you dont find any vacuum leaks or misfire sparkplug wire or even worn out sparkplugs, As for 1870 The front switch for the 4x4 insept that they do in fact take on  corrosion so look at the terminal end ( this is for the front differential)