Oil Pressure Gauge Question

John Scoggins

John Scoggins

TJ Enthusiast
Joined
Oct 23, 2018
Messages
528
Location
Houston, TX
Having the oil pressure gauge problem that seems to be common to our TJ's. The gauge goes to 0 at certain times at idle, then back to "normal" when RPM's are added. I had this issue about a year ago and fixed it (so I thought) by cleaning the two connectors on the back of the Instrument Cluster. I have cleaned the connectors again but the problem still exists. I have let the motor idle for 45 min while indicating 0 PSI with no engine noises so I assume that I have pressure at idle (will put my manual gauge on it this weekend to confirm). I know the PCM the Instrument Custer "gauge" is really an idiot light that is either at 0 or a little past the middle when the oil pressure is 6PSI or more.

While messing with it last night for a bit I found that if the gauge is indicating pressure while the engine is idling, if I disconnect the connector from the Oil Pressure Sending Unit the gauge will still indicate pressure for as long as the Jeep idles. When I turn off the engine and remove the key wait 5 min and start it back up (connector still disconnected) the gauge will then indicate 0PSI and the check Gauges Light indicates, if I plug the connector back in while running the gauge will still show 0PSI until I turn off the Jeep remove the key and start it back up.

Has anybody has this happen? According to the manual there is a time delay between when the sensor changes and the gauge displays but that is 12 seconds, I let it run disconnected for 30min and the gauge always showed pressure until I turn off the Jeep and turned it back on. It seems that the PCM is getting a signal that there is oil pressure when the sensor is unplugged until it is power cycled (and vise-versa).

I have ordered a Mopar sensor (P/N 5149097AA) but not so sure this will fix the issue.
 
While looking at the manual I notice that the Oil Pressure Sensor for the 4.0L shows that is has a variable resistance ( as opposed to the 2.4L that seems to show a switch). Has anyone actually put a meter on the output to see if it does in fact send out variable resistance? I am going to see tonight if it does by probing pin 23 on the C2 connector to the PCM just for curiosity sake and if it does I might just make a resistor pack to simulate oil pressure (so the Instrument Cluster gauge will show pressure) and add a real pressure gauge, installing the gauge in the Tuffy console.
 
The usual cause of that problem is a defective oil pressure sender which is mounted adjacent to the oil filter. Make sure NOT to install a store brand oil pressure sender as they often give problems. It took 3 different Duralast oil pressure senders from Autozone one Sunday before I finally got one that worked properly. Your best bet is to replace it with a Mopar.
 
  • Like
Reactions: Jeanfi007 and John Scoggins
Have you tried ANY new or different Oil pressure sensors yet?
Click to expand...

Yes, forgot to add that in the post, I had an Autozone one sitting around from last year I never installed so I did install it and got the same results, but like Jerry stated I need to get a Mopar one to start with, which I am.

Your best bet is to replace it with a Mopar.
Click to expand...

Ordering one now....
 
Also, does anybody know which of the four screws behind the oil pressure gauge is the signal and what voltage is sent to put the gauge in the center?
If I go ahead and install a real gauge I might need to send voltage to the gauge to have it stay in the center so it will not be at zero.
 
Most all electric oil pressure gauge systems are variable output. The change in voltage is what moves the needle. I am not up on the TJ system, but they all act similarly. May measure voltage change, resistance change, but basically all the same. The sending unit or what it mounts in gets sludge built up inside causing the signal output to go off.
 
It's not the sender that causes the constant mid-scale oil pressure indication on newer TJs, the system was just reprogrammed to always so that mid-scale indication so long as the real oil pressure is within acceptable limits. The sender is a variable resistor for all model year despite sometimes being described as a switch. The factory reprogrammed it in later model years because new buyers were complaining to their dealers the oil pressure was going up & down and the dealers couldn't convince them it was normal. For many TJ buyers it was their first vehicle with an oil pressure gauge and they didn't understand oil pressure is supposed to go up & down in direct step with engine rpms. 10 psi per thousand engine rpms is the usual rule-of-thumb for good acceptable oil pressure.
 
Last edited:
Cool, thank you Jerry that is what I was thinking so if I wanted to add a real gauge all I would need to do if figure the signal voltage to the gauge that puts it in the middle and send that to the instrument cluster, thus keeping the IC gauge so the check gauges light will not come on.
I can just probe the IC tonight behind the oil pressure gauge when it is working to find the signal voltage that puts the gauge in the middle I would figure.
 
John Scoggins said:
Cool, thank you Jerry that is what I was thinking so if I wanted to add a real gauge all I would need to do if figure the signal voltage to the gauge that puts it in the middle and send that to the instrument cluster, thus keeping the IC gauge so the check gauges light will not come on.
I can just probe the IC tonight behind the oil pressure gauge when it is working to find the signal voltage that puts the gauge in the middle I would figure.
Click to expand...
I personally wouldn't bother since we know the real oil pressure is ok so long as the factory gauge is mid-scale.
 
I've been having a similar problem lately. Is the 5149097AA part number mentioned earlier for the 4.0 engines? I looked up 4868672AA in the 2003 parts list and it appears to be discontinued. Was it superseded by the 5149097AA part? Yes, the 5149097AA part number supersedes the older 4868672AA number.

I haven't had the gauge drop to 0 while running but a handful of times recently it has stayed at 0 during startup and the check gages light comes on. Everytime so far, the gauge has come up on subsequent starts after shutting it off. I also notice the engine seems to crank a bit longer after it has exhibited the stays on 0 at startup symptom. This happened today when I was going to drive it and the check engine light was on after the gauge finally came up to normal.

Any chance a weak battery could be causing the sensor or gauge to behave erratically?
 
Last edited:
  • Like
Reactions: CODE5
Top Bottom
Back