Question about 1998 Chevrolet Malibu
A reference circuit is a reduced voltage(less than 12) that is current controled
without it your car may suddenly accelerate smply by you turning
your heater or Ac on (the battery voltage changes )
it's used on many cars for the sensors like the throttle posisition
if the fault code says you lost it
you got a shorted wire or sensor somewhere on the engine
consult your vehicles engine wire diagram to see what sensors run on 5 volt ref
then start lookin and unhookin
(chiltons avail in most public librarys has a good wire diagram)
Posted on Jul 15, 2009
12v and negative are supplied to the computer . Some components only need 5 vols. The computer will reduce the voltage to those components. Some components need 12 volts. Most of these are supplied directly from the battery to fuse block to relay or no relay and then to component. The computer has the ability to supply a modulated or constant ground as needed to all the components. If you lost the 5v reference you most likely need a PCM if the 12 and ground are good going to the PCM. Same for the grounds. If you lost the ground and the 12v is good coming from the fuse block.
Posted on Jul 15, 2009
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Posted on Jan 02, 2017
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Jun 10, 2017 | Cars & Trucks
The exhaust gas recirculation (EGR) valve
The fuel tank pressure (FTP) sensor
The throttle position (TP) sensor
These 5-volt reference circuits are independent of each other outside the PCM, but are bussed together inside the PCM. Therefore a circuit condition on one sensor 5-volt reference circuit may affect the other sensor 5-volt reference circuits. The PCM monitors the voltage on the 5-volt reference circuit. If the PCM detects that the voltage is out of tolerance, DTC P1635 sets.
If any sensor using a 5-volt bias voltage, such as the intake air temperature (IAT) sensor or fuel sensor, is shorted to voltage, DTC P1639 may set in addition to DTC P1635.
For an intermittent condition, refer to Intermittent Conditions .
Does the vehicle start an run ?
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