Bad sensor?
I'm not sure how this thing can have "low voltage". As far as I know, the switch opens to ground at 0psi and the VCM cuts the engine... and there is no voltage to reference.
I think I hit these also, but never the 0520 Malfunction code.
Again, I think I remember these, but I've cleared the codes maybe 5 times and it pops up almost immediately in HPT vcm scanner [immature] and takes a while for the CEL to pop.
DTC P0521 Engine Oil Pressure Sensor/Switch Circuit Range/Performance
DTC P0523 Engine Oil Pressure Sensor/Switch Circuit High Voltage
I roll on steelies. Work-in-progress daily-sleeper potential.
http://www.j-body.org/classifieds/engine/60493/
First look at the relationship of the fuel Pump Relay and the Oil Pressure switch.
Just as you had stated they are wired in parrallel with eachother utilizing the same 12v power source as well does the ECM. Now notice circuit 465 going from the request terminal of the FP Relay to ECM pin# F6 Labeled FP Relay Control. That is the circuit the ECM uses to energize the relay to close the switch to power the fuel pump. Now lets look at the Oil Pressure switch. Notice that it is similair to a relay/crossed with a variable resistor. Notice the location of pin A that leads to the Inst Cluster. When the sensor detects oil pressure it changes the resistance which is monitored by the guage or light on one side of the switch. That half energizes the switching of the other half ( So that switch can fail and store a PO520 and the guage or light still work properly on later models utilizing the OBD2 diagnostics systems). Now at this point it seems that the ECM powers up the fp relay and then oil pressure opens the OP switch and both power sources run at the same time powering up circuit 120 through the fp fuse to the fuel pump. That is where the mistake is made... Now look at the ECM pin# B12. Notice it is labeled Oil Pressure Input and not FP Input. That is where the ECM monitors for adequate oil pressure. Now notice the wire attached to that pin is a gray wire of circuit 120 (the very same circuit that powers the fuel pump). Now if you trace that wire it leads to splice#127 where it monitors the voltage supplied to the fuel pump.Now use some common sense... How can oil pressure be monitored on a wire that is powered up by the fp relay and the OP switch at the sametime? It can't... This is how it works... The ecm powers up the fp relay providing power to the fuel pump to start the engine. Then when oil pressure comes up and the OP switch closes the additional 12V power source causes a spike in the current flowing to the fuel pump that is monitored at pin# B12 of the ECM. The ECM then cutsoff fp relay request at pin# F6 and disables the fp relay. At that point all power flows through the OP switch to fuel pump allowing pin# B12 to monitor oil pressure and not fp relay voltage. So you should be able to see now that if the OP switch failed the engine would die from the fuel pump being shut off. Also if the engine was to suddenly stop ( as in a crash) the fuel pump is immediately killed very similairly to Ford's fuel inertia switch system.. IT IS A SAFETY ISSUE TO PREVENT FIRE AFTER A COLLISION.
First Off, I didn't read your post completely yet so don't yell.
ECU Diagram / Oil Pressure Switch
According to Mitchell1 DIY, the oil pressure switch is just a single wire going straight to the ECU/VCM (Which ever you prefer)
The FP has 2 relays as I recall, and I am pulling from the main under hood relay to power my gauges, and the secondary relay may be in backwards. I'll pull the gauge power from somewhere else and double check the relays to be sure. Also let me know if you want me to put the other 2 ECU diagrams up.
Edited 3 time(s). Last edited Tuesday, May 07, 2013 1:36 PM
I roll on steelies. Work-in-progress daily-sleeper potential.
http://www.j-body.org/classifieds/engine/60493/
Yeah I'm pulling power from the heater blower relay directly into the cabin. After looking under the fuseblock, all the IGN HOT leads are someway or another connected to the FP relay, and with the feedback from multiple gauges, I'm sure it's doing something.
If the problem doesn't go away after I find a new +12 for my gauges I'll post back any findings. I think the radio harness ignition wire should be ideal. At least for switching a relay, although then I need to find a +12v constant wire. You think I can get away with just pulling from the ign hot radio wire for the gauges?
I roll on steelies. Work-in-progress daily-sleeper potential.
http://www.j-body.org/classifieds/engine/60493/
You have your on/off voltages backwards. Theres a spring and plunger inside of the switch. The plunger receives hot from the PCM and the contact of the body goes to ground. The plunger and contact are together when there is no oil pressure. This creates a circuit which the PCM sees and trips the oil pressure light via serial data. When you have pressure the plunger isnt making contact. The circuit is open and you have no light. You really cant reference a single wire switch.
What Jason in describing as the switch is actually an oil pressure sensor which is a solid state pressure transducer that actually varies the voltage as the plunger is pushed toward the ground. A sensor has a ref voltage wire.
Im not really sure what you have going on with your gauges or what not because nothing has been mentioned unless Im missing a thread somewhere. But really the only symptom of a bad oil pressure switch is a flickering oil pressure light.
Now that I re-read what you posted youre right. Just worded weird. Circuits close to ground.
As far as a good place to pull switched power for your gauges I always liked tapping into the windshield wiper circuit. Its nonessential to the car running and is relatively low amperage. Just make sure you tap on the outgoing side of the fuse so you dont burn your car down.
Brian wrote:Now that I re-read what you posted youre right. Just worded weird. Circuits close to ground.
As far as a good place to pull switched power for your gauges I always liked tapping into the windshield wiper circuit. Its nonessential to the car running and is relatively low amperage. Just make sure you tap on the outgoing side of the fuse so you dont burn your car down.
I always fuse twice when adding circuits! In-line fuse after the Fuse Block pull. Thanks for the wiper idea, that's what I'm going to do. I also need a headlamp switched +12 source to dim my glowshift gauge and to power a small bulb in the boost gauge. (I tried to pull from the dimmer switch and it does some weird crap) I can figure it out, just wondering if there's any popular spot.
Also theres no thread or detail about my gauges besides this, so no you didn't miss anything ;|
I roll on steelies. Work-in-progress daily-sleeper potential.
http://www.j-body.org/classifieds/engine/60493/
jason norwood wrote:First look at the relationship of the fuel Pump Relay and the Oil Pressure switch.
Just as you had stated they are wired in parrallel with eachother utilizing the same 12v power source as well does the ECM. Now notice circuit 465 going from the request terminal of the FP Relay to ECM pin# F6 Labeled FP Relay Control. That is the circuit the ECM uses to energize the relay to close the switch to power the fuel pump. Now lets look at the Oil Pressure switch. Notice that it is similair to a relay/crossed with a variable resistor. Notice the location of pin A that leads to the Inst Cluster. When the sensor detects oil pressure it changes the resistance which is monitored by the guage or light on one side of the switch. That half energizes the switching of the other half ( So that switch can fail and store a PO520 and the guage or light still work properly on later models utilizing the OBD2 diagnostics systems). Now at this point it seems that the ECM powers up the fp relay and then oil pressure opens the OP switch and both power sources run at the same time powering up circuit 120 through the fp fuse to the fuel pump. That is where the mistake is made... Now look at the ECM pin# B12. Notice it is labeled Oil Pressure Input and not FP Input. That is where the ECM monitors for adequate oil pressure. Now notice the wire attached to that pin is a gray wire of circuit 120 (the very same circuit that powers the fuel pump). Now if you trace that wire it leads to splice#127 where it monitors the voltage supplied to the fuel pump.Now use some common sense... How can oil pressure be monitored on a wire that is powered up by the fp relay and the OP switch at the sametime? It can't... This is how it works... The ecm powers up the fp relay providing power to the fuel pump to start the engine. Then when oil pressure comes up and the OP switch closes the additional 12V power source causes a spike in the current flowing to the fuel pump that is monitored at pin# B12 of the ECM. The ECM then cutsoff fp relay request at pin# F6 and disables the fp relay. At that point all power flows through the OP switch to fuel pump allowing pin# B12 to monitor oil pressure and not fp relay voltage. So you should be able to see now that if the OP switch failed the engine would die from the fuel pump being shut off. Also if the engine was to suddenly stop ( as in a crash) the fuel pump is immediately killed very similairly to Ford's fuel inertia switch system.. IT IS A SAFETY ISSUE TO PREVENT FIRE AFTER A COLLISION.
so what would happen if you unplugged the oil pressure sensor and left the plug dangling?
also, if I'm understanding what you're saying correctly, the OP switch controls the voltage to the fuel pump?
so, if I pull my fuel pump relay, my car will stay running? is that what you're saying here?
Eric Knight wrote:Brian wrote:Now that I re-read what you posted youre right. Just worded weird. Circuits close to ground.
As far as a good place to pull switched power for your gauges I always liked tapping into the windshield wiper circuit. Its nonessential to the car running and is relatively low amperage. Just make sure you tap on the outgoing side of the fuse so you dont burn your car down.
I always fuse twice when adding circuits! In-line fuse after the Fuse Block pull. Thanks for the wiper idea, that's what I'm going to do. I also need a headlamp switched +12 source to dim my glowshift gauge and to power a small bulb in the boost gauge. (I tried to pull from the dimmer switch and it does some weird crap) I can figure it out, just wondering if there's any popular spot.
Also theres no thread or detail about my gauges besides this, so no you didn't miss anything ;|
Which wire on the dimmer did you tap off of? Im guessing the dimmer works by varying resistance and throwing extra load in at the wrong spot would probably make it do weird stuff.
Im looking at my Haynes manual and it looks like theres a yellow wire leading into the dimmer that should do what you need. But my electrical-diagram-foo is weak.
