Question1996 neon, 2.0L, SOHC, intermittent "bucking" or "hiccuping". Check engine light is on but goes out when it bucks. Fault codes are-- 12,21,43... Believe it is the fuel system, not 100% but pretty confident. only acts up after driving for a little while, or when the car warms up. Thanks a lot!
AnswerHi Justin,
The 21 code says either or both oxygen sensor signals are not changing as expected. Those come into play when the engine warms up so that is consistent as a possible cause. The sensors have 4 wires: black is a chassis ground wire, black/light blue is a signal ground wire that should be continuous to pin 43 of the pcm, dark green/orange is 12v supply which should be present when the engine is running; and the upstream sensor signal black/dark green goes to pin 30 of the pcm, and downstream sensor signal tan/white goes to pin 51 of the pcm. So check the continuity of the wires and that the 12v supply is present. If that checks out and the sensor wires look good, then I would start by replacing the upstream sensor.
The 43 says you have misfiring, but not why or which cylinder(s). There are a long list of possibilities, but perhaps this will go away if you solve the oxygen sensor situation.
The 12 code is common and says the battery supply was disconnected recently.
Roland
