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Discussion Starter · #1 · (Edited)
I recently went on the adventure of diagnosing why my oil pressure gauge on my 2001 WJ has been acting up. When the problem first occurred I just replaced the sensor with a genuine MOPAR one. Problem fixed....for only three months, then the problem returned. I decided to dive in and do some more serious investigating.

I have posted everything I found here. Hopefully this info will point folks in the right direction when dealing with this same issue.
To perform all the diagnostics and/or remove the sensor you need these tools:
--A good quality Digital Multimeter for testing circuitry
--1 1/16" Deep socket for removing/installing the Oil pressure sensor
--Tools for gaining access to the PCM, you need to remove the coolant reservoir on a 4.7L
--Fittings, size 1/4" NPT for attaching tubing
--Bottle/oil pan for catching oil
--Mechanical Oil Pressure Gauge with 1/4" NPT fittings, mine is a U.S. General (Harbor Freight) #92687


Since I had just replaced the sensor, I figured there was either a serious oil pressure problem in the engine or the circuit to the sensor was bad somewhere.


To ensure the engine was not starving of oil:
1. I connected a mechanical oil pressure gauge to the engine using the same port the electrical sensor uses. Pressure read normal, up around 40 to 50 psi, even got as high as 60+ when the RPMs were up pretty high.
2. I installed a small fitting into the port and ran tubing from the port to a bottle on the ground. I cranked the engine until it started, gave it about 1 second, and then immediately turned it off. There was PLENTY of pressure and flow as it completely filled a 16 oz. bottle and made a mess in less than 2 seconds. (This can also blow out any debris that may blocking good flow/pressure)
3. I also listened for any noises that come from an engine that's not getting oil.....but nothing, no ticking, no clicking, nothing out of the ordinary. The engine ran great.

After feeling much relief knowing the engine was fine oil-wise I moved on to the circuitry for the oil pressure sensor.

If there is indeed a mechanical problem and your engine is not getting oil DO NOT run your engine for any longer then ABSOLUTELY necessary for testing and DO NOT drive it. Tow it home if anything. An engine without oil does not have to run for very long to cause serious damage.


I found a great post on JeepForums that copies the diagnosis procedure from a service manual for testing the circuitry. The info is in post #4:
http://www.jeepforum.com/forum/f96/check-engine-light-low-oil-pressure-1371678/
The info is for a later model Jeep that actually throws a DTC code when the oil pressure is out of acceptable range. Regardless, the testing procedures are the same. I also found some comprehensive testing information on another website for a Chrysler 300C. The circuitry is still the same except for the pin-out on the PCM connector.
There are three connectors that feed the PCM. They are all the same shape but each has a different color tab, black, gray, or white. The image below shows the correct pin-out of the oil pressure sensor signal for a 2001 WJ with either engine on the connector with the White Tab:




And here is the Oil Pressure Sensor Connector Pin-Out from my service manual:



If your Jeep is a newer model then the PCM pin-outs will probably be different as well as the circuit reference numbers (G60, K4, K6). Consult a Service Manual for your year and model for correct information. And/or send me a message and I'll try to give you a hand.

Here are the diagnostic procedures I found online (circuit reference numbers have been translated to match my year and model):


------------DIAGNOSTIC PROCEDURES-------------
Possible Causes:
-(G60) ENGINE OIL PRESSURE SENSOR SIGNAL CIRCUIT SHORTED TO BATTERY VOLTAGE
-RESISTANCE IN (G60) ENGINE OIL PRESSURE SENSOR SIGNAL CIRCUIT
-(G60) ENGINE OIL PRESSURE SENSOR SIGNAL CIRCUIT SHORTED TO GROUND
-RESISTANCE IN (K6) 5-VOLT SUPPLY CIRCUIT
-(K6) 5-VOLT SUPPLY CIRCUIT SHORTED TO GROUND
-RESISTANCE IN THE (K4) SENSOR GROUND CIRCUIT

1. This test applied only to newer Jeeps that throw a code when the oil pressure is out of allowed range. It just tested to ensure the code was still being thrown and was not an Intermittent problem.

2. (G6, G60) ENGINE OIL PRESSURE SENSOR SIGNAL CIRCUIT SHORTED TO BATTERY VOLTAGE
Turn the ignition off. Disconnect the PCM harness connectors. Disconnect the Engine Oil Pressure Sensor harness connector. Ignition on, engine not running. Measure the voltage on the (G60) Engine Oil Pressure Signal circuit in the Engine Oil Pressure Sensor harness connector.
Is the voltage above 0 volts?
Yes - Repair the short to battery voltage in the (G60) Engine Oil Pressure Signal circuit.
No - Go To Test 3

3. ENGINE OIL PRESSURE SENSOR
Turn the ignition off. Connect the PCM harness connectors. Ignition on, engine not running. With a scan tool, monitor the Engine Oil Pressure Sensor voltage. Connect a jumper wire between the (K4) Sensor Ground circuit and the (G60) Engine Oil Pressure Signal circuit. NOTE: Engine Oil Pressure voltage should change from approximately 4.5 volts to less than 0.5 of a volt. Is the voltage reading within the listed specification when the jumper wire is installed?
Yes - Replace the Engine Oil Pressure Sensor.
No - Go To 4
NOTE: Remove the jumper wire before continuing.

4. EXCESSIVE RESISTANCE IN THE (G60) ENGINE OIL PRESSURE SIGNAL CIRCUIT
Turn the ignition off. Disconnect the PCM harness connectors. CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.
Measure the resistance of the (G60) Engine Oil Pressure Signal circuit from the Engine Oil Pressure Sensor harness connector to the appropriate terminal of special tool #8815.Is the resistance below 5.0 ohms for each circuit?
Yes - Go To 5
No - Repair the excessive resistance in the (G60) Engine Oil Pressure Signal circuit.

5. (G60) ENGINE OIL PRESSURE SIGNAL CIRCUIT SHORTED TO GROUND
Measure the resistance between ground and the (G60) Engine Oil Pressure Signal circuit Engine Oil Pressure Sensor harness connector. Is the resistance below 100 ohms?
Yes - Repair the short to ground in the (G60) Engine Oil Pressure Signal circuit.
No - Go To 6

6. EXCESSIVE RESISTANCE IN THE (K6) 5-VOLT SUPPLY CIRCUIT
Measure the resistance of the (K6) 5-volt Supply circuit from the Engine Oil Pressure Sensor harness connector to the appropriate terminal of special tool #8815.Is the resistance below 5.0 ohms?
Yes - Go To 7
No - Repair the excessive resistance in the (K6) 5-volt Supply circuit.

7. (K6) 5-VOLT SUPPLY SHORTED TO GROUND
Measure the resistance between ground and the (K6) 5-volt Supply circuit in the Engine Oil Pressure Sensor harness connector. Is the resistance below 100 ohms?
Yes - Repair the short to ground in the (K6) 5-volt Supply circuit.
No - Go To 8

8. EXCESSIVE RESISTANCE IN THE (K4) SENSOR GROUND CIRCUIT
Measure the resistance of the (K4) Sensor Ground circuit from the Engine Oil Pressure Sensor harness connector to the appropriate terminal of special tool #8815.Is the resistance below 5.0 ohms?
Yes - Go To 9
No - Repair the excessive resistance in the (K4) Sensor Ground circuit.

9. PCMNOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.
Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits. Were there any problems found?
Yes - Repair as necessary.
No - Replace and program the Powertrain Control Module per Service Information.


--------------------------------------


Whew......After doing all these tests I determined that the problem was indeed the sensor since all the circuitry checked out. This means a genuine MOPAR sensor went bad on me in only 3 months....
The bad sensor:
1. Had a signal voltage of 0.13v when the engine was running.
2. Had a signal voltage that did not respond to a change in engine RPMs


I replaced the sensor with one from Autozone with a lifetime warranty. If it ever goes bad again I can just take it in and get it replaced. Problem fixed! Oil pressure gauge working normally again.

After replacing my sensor the voltage from the sensor signal circuit:
1. Reads 0.71v with the engine off
2. Reads 3.68v with the engine running and the oil pressure gauge around 50psi
3. Changed as engine RPMs increased and decreased. It reached upwards of 4.5v+ when around 3K+
RPMs


Keep in mind that your voltages will most likely be different depending on the draw on your electrical system, your alternator voltage output, and your battery voltage.


Another thing to check when diagnosing your oil pressure problem was brought up by JDRM.
Here is his post:
I have a 2002 Durango with the 4.7L engine and thought I would share what caused my no / low oil pressure problem.

After flushing the engine, changing the PCV Valve, changing the oil
pressure sending unit, changing the oil and filter many times and
searching the web. I finally stumbled across the problem (mine others
may be different). Every time I put a mechanical gauge on it the
pressure was ok. The problem occurred mostly at higher RPM's.. When
it went to "check gages" I could shut off the engine then on restart
oil pressure would return to the safe level but not to where it
normally runs. Letting the Durango sit over night the oil pressure
would return to the normal pressure. I never had a mechanical gauge
available when acting like this.

It's related to oil emulsion accumulation inside the engine oil fill
housing. Nowhere in any of my manuals does it call for pulling the
baffle in the oil fill housing and cleaning it and inside the
housing. The accumulation sometimes blocked the PCV port causing the
Low / no oil pressure.

Hope this helps someone




Regards
Thanks JDRM!


I hope this helps some folks! Feel free to ask any questions or post anything else you feel would help.
Thanks for reading!
-JeepBoy
 
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