GM DTC code P1639

Tiny
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
Sunday, December 31st, 2017 AT 3:35 AM

2 Replies

Tiny
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
Tiny
STEVE W.
  • MECHANIC
  • 13,414 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.
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Sunday, December 31st, 2017 AT 9:12 AM

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