Do you know anything about ECM five volt reference circuit's ?
DTC P0641: 5-Volt Reference 1 Circuit
The engine control module (ECM) has 3 internal 5-volt reference busses called 5-volt reference 1, 5-volt reference 2, and 5-volt reference 3. Each reference bus provides 5-volt reference circuits for more than one sensor. Therefore, a fault condition on one 5-volt reference circuit will affect the other 5-volt reference circuits connected to that reference bus. The ECM monitors the voltage on the 5-volt reference busses.
The 5-volt reference 1 bus provides 5 volts to the following sensors:
• The manifold absolute pressure (MAP) sensor
• The clutch apply sensor
• The fuel rail sensor
• The fuel tank pressure (FTP) sensor
• The intake air pressure and temperature sensor
You have a shorted sensor more then likely or wiring problem . Suggest you watch this video .
How to check the 5v reference circuit for short to ground Cadillac
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