GM DTC code P1639

BILLY MILLER

MEMBER
2002 PONTIAC FIREBIRD
3.8L
V6
TURBO
2WD
AUTOMATIC
90,000 MILES

I got a check engine light on, GM code P1639 five volts fer, circuit 2. The dealer changed the AC pressure sensor. The light came back on would live data show if something is too high or low? Or the freeze frame shows what caused the light to come on? It does not show a code, but when I look at the o2 sensor data it shows rich to lean response to lean to rich switches response ratio fail. What would cause that? My manual shows codes like 23 and 25 instead od P ____ codes. Any help will be appreciated. Thanks

2 Replies

ASEMASTER6371

MECHANIC
52,797 POSTS

Good morning.

Below is the flow chart for the code.

Roy

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Sunday, December 31st, 2017 AT 4:20 AM

STEVE W.

MECHANIC
13,576 POSTS

Have seen this code pop up when the harness directly behind the ECM gets damaged by a screw. The tip of the screw rubs through the wiring and shorts it out. You remove the ECM and can check the harness where it comes out of the firewall. If that is not it then look at the TPS and fuel tank pressure sensors. They use the same five volt reference circuit. The O2 sensors have nothing to do with this code.