My check engine light is on. The VCM says: PAO.

car drives runs perfectly and transmission and headlamp?
does CEL glow key on? check engine lamp(it self tests then)
fuses first. F4 = gage fuse/ 6 fuses to make VCM run.
scan the PCM
check for 12vd top the cluster power pins.
the VCM sends speed data (serial ) to the cluster brain.
speed vss1 is digital sensor, on trans.
tach is pure VCM/PCM signal sent to cluster.
Id say F4 blow. if car drives ok, not told wow./

Is the check engine light lit ? Any DTC'S - diagnostic trouble codes ? What engine ? 4.3 L vortex . Leaking fuel pressure regulator under the upper intake manifold . Leaking fuel injectors ! Ignition timing problem . How does the engine run ? Who installed the plugs an wires ? are they right ? Fuel pressure leak down test, fuel injector balance testing . Check distributor drive gear an slop in the shaft . Did you have distributor out ? Is it in the proper position ? What cylinder is misfiring ? engine mechanical problem ! What do spark plugs look like ? fouled , soaked with fuel . Do a engine compression test .
The camshaft drives the distributor shaft which rotates providing a spark to the correct cylinder by way of the cap and rotor. The camshaft position sensor functions much like the crankshaft sensor previously described but provides only a 1x signal to the VCM. That is, for every 2 rotations of the crankshaft, there is 1 rotation of the camshaft. Note that the CMP sensor will not affect driveability. The sole purpose of the CMP sensor is to provide the VCM with the necessary information for the misfire DTCs.

Check ignition module/coil(s) and check for correct fuel pressure.

Okay, hey, the fuel pump circuit. With key on, the pump should turn on for about two seconds to put pressure in the line and in the fuel rail on the engine, where the fuel injectors are. When the engine is cranking, the pump is turned on again by the vcm (Vehicle Control Module-the engine computer) signaling the fuel pump relay, just as it did with key on. After the engine is running, the pump is kept on, usually by the oil pressure switch.
No fuel pressure? Then the pump is not turning on, or the fuel filter is completely blocked-which is rare.


You can start at the Underhood Fuse Block. Here is found the fuel pump relay and the fuse for the pump. The fuse is designated ECM-B Fuse and it's 20 amp. If the fuse is good, put your finger on the fuel pump relay. Now have a helper turn the key to on, not start. If the circuit is good to this point, you should feel movement- a slight click. If you feel nothing, and the fuse is good, then the VCM is not sending a signal to the relay OR there is a wiring problem from one side of the relay to ground. If no click or movement under your finger-you will need professional help to diagnose further-checking of the signal from VCM and/or checking the ground wire for that side of the relay.
If you definitely feel a click at the pump relay, and the fuse is good, the power to the pump is sent out from there on a gray wire. Get under the vehicle at the rear and find the electrical connector for the gas tank, and pull it apart. Now you need a test light or voltmeter to check for power on the gray wire in the connector. You might miss the two second signal with key on, so have your helper hold the key in start. While the engine is cranking, the gray wire should have power-battery voltage. If it does not, big problem: possibly a broken wire or short from pump relay to there at the gas tank.

If the gray wire has power with engine cranking, you're almost home: Either the pump has definitely failed OR the ground for the fuel pump is bad. The ground wire is black and it shares the same ground point as your rear exterior lights, so if the lights work, the ground can be assumed to be good also for the fuel pump. And then you need a new fuel pump. But check the gas tank connector carefully for any sign of corrosion, loose terminals, anything like that amiss. Not likely, but check anyway-you don't want to put in a new pump and then find a loose connection! Good luck.

Codes

Print
Stored fault codes may be erased from memory at any time by removing power from the VCM for at least 30 seconds. It may be necessary to clear stored codes during diagnosis to check for any recurrence during a test drive, but the stored codes must be written down when retrieved. The codes may still be required for subsequent troubleshooting. Whenever a repair is complete, the stored codes must be erased and the vehicle test driven to confirm correct operation and repair.

WARNING The ignition switch must be OFF any time power is disconnected or restored to the VCM. Severe damage may result if this precaution is not observed.
Depending on the electrical distribution of the particular vehicle, power to the VCM may be disconnected by removing the VCM fuse in the fusebox, disconnecting the in-line fuse holder near the positive battery terminal or disconnecting the VCM power lead at the battery terminal. Disconnecting the negative battery cable to clear codes is not recommended as this will also clear other memory data in the vehicle such as radio presets.
The following are the codes for the 1994-95 models with the OBD I and OBD II systems.
See Figure 1 through 6

Fig. Fig. 1: DTC chart for 1994 ECM models

Fig. Fig. 2: DTC chart for 1994 PCM models

Fig. Fig. 3: DTC chart for 1994-95 VCM models

Fig. Fig. 4: DTC chart for 1995 PCM models

Fig. Fig. 5: DTC chart for 1995 VCM-A models

A vehicle control module (VCM) or powertrain control modules' (PCM) electronically erasable programmable read only memory (EEPROM) contains data essential to running the engine and transmission. The VCM/PCM stores critical preprogrammed data within the EEPROM, this data remains even if the vehicles' battery is disconnected. At power up the VCM/PCM checks the integrity of this data. If the checksum of the EEPROM does not match a predetermined value, DTC P1621 will set. The DTC will also set if the VCM/PCM is unable to correctly read or finds corrupt data from the EEPROM. GM recommends testing/replacement of the VCM/PCM using required equipment by a qualified technician for this type of VCM/PCM memory performance fault condition.

my manual says fuel fail 14 deals with yourr coolant temperature sensor is no in operating range

dear,


The fuse ecm b it tied to the fuel pump, PCM, and VCM.
Fuel pump could have an internal short
check it by the way...

regards,

chances atre if it was the whole board you whould not have a speddometer or anything. there are seperate modules on the board it sits behind the dash. when removing it you want to be careful. if you have a static charge and it discharges on the board you will fry it. i use a bracelet that has a longe wire with an alligator clip and i attach it to a ground that way the charge will ground to the vehicle body and not the board. please rate this thanks