Community Forums

reosw · 01-14-2021, 10:09 AM

Ive seen this issues in various places in the forum, so forgive me if this
is repetitive. Have single wire OP sender and recent issue with OP gauge going to 55 psi the moment ignition is turned on...seems the sender is simply a switch, but what makes no sense is the gauge going full scale, then intermittently dropping back to 55. Also getting check engine light (running scan today) and flashing OP light and buzzer. Oil level is fine. Have a new sender ready to install, but cant figure out what is making the gauge go full scale....an on-off signal from the sender would not seem capable of doing this. Scratching my head.

Lowflyer1 · 01-14-2021, 01:54 PM

What model, year and engine do you have?
A switch vs sender are easy to tell apart.

The switches are smaller as they are basically just a diaphragm and a spring and should also have an opening or closing pressure depending on type.

Senders are larger and should have a pressure range.

reosw · 01-14-2021, 03:14 PM

Top right...single wire....have owned the motorhome for 10 years, so no changes to the sender, ECU or wiring.....have a new one on hand. Ran silverleaf diagnostics and got an oil pressure low voltage message. Check engine light had been on, OP gauge pegged and blinking OP idiot light and buzzer. Cleared code, started engine, and no issues, thus some transient problem seems to be triggering the false readings. Also, Silverleaf is showing a constant 55 PSI as it has for years, even when analog gauge was pegged. Is there more than one OP sender ? 2003 Cummins ISL 400.

Lowflyer1 · 01-15-2021, 05:54 AM

reosw, can you add your coach year, make and model to your signature, should be the same info you provided to get the new switch. Others with similar coach may be able to provide input.
Adding signature: At the top left "User CP --> Settings & Options --> Edit Signature".

There are many different oil pressure switches and senders, gages etc. based on the system on your coach so I don't want to even try to guess what the problem may be other than you can probably rule out the switch as sounds like you have a switch operated idiot gage. All a switch does is either opens or closes the circuit to ground (since you only have one wire) when the oil pressure is around 5-10 psi. Then the electronics drive the gage up to the set point. I assume your normal indication of 55psi is somewhere in the mid-range. The actual oil pressure on any engine will vary anywhere from maybe 10 psi to 60 or more depending on temp, RPM etc.

But to start, you can compare the resistance on the new switch to the old (whether open or closed) as they sit on a table. They should be about the same.
If you have a way to hook these up to like 10 psi, you can check if they are again the same.
You can compare the readings on the old switch as it is in the engine as there will be some oil coming out if you take the switch out:
Engine off - no pressure reading, engine on - pressurized reading.
They should be about the same.

c_oneil · 01-15-2021, 07:04 AM

From your public profile I see you have a Newmar but no year is listed. If changing out the switch doesn't fix the problem you should post something on the Newmar owner forum. It could be an issue with your gauge cluster or the ECU data wiring since you have a CEL as well. For instance on my coach the Cummins engine data from various engine switches and sensors is transmitted via a digital data bus to the ECU plus a gauge cluster computer that controls the gauges. Your dash gauge may be an analog gauge but at some point it could be using a digital data network for its input.

reosw · 01-16-2021, 07:59 AM

I do have the idiot gauge....reads the same no matter engine speed.....but when the malfunction began, the gauge would go to the the 55ish PSI position before the engine was started, once the ignition switch was on. Second major issue was gauge would peg and oil pressure idiot LIGHT would flash along with a buzzer. It then seemed to reset itself, but the last time I started, I got check engine light, pegged gauge, buzzer and light. Also, my SilverLeaf systems was also showing 55 PSI. Diagnostics showed Oil Pressure sensor, low voltage condition. Reset code, restarted an all was fine, so it is obviously a transient issue. OP, Switch, ECU, wiring, etc....hard to establish. At least it seems actual OP is not the issue. Will run again today to see what happens.

jacwjames · 01-16-2021, 08:14 AM

What engine do you have.

I have a 8.3L ISC in a 2002 Monaco. The engine actually has two oil pressure sensors, one for the dash gauges and one for the ECM. Both mine are proportional and read what the oil pressure is. I know that replacement from Cummins (unless I can find the original) would be a switch type either reading good or bad. I also have a silverleaf and rely on that for monitoring my oil pressure which ranges high on startup but as engine heats up drops and when hot at low RPM can bump to ~20psi but this is within recommended operating parameters.

If your rig has a Cummins engine you can join the quickserve.com site, create an account and register your engine. You will have lots of information on maintenance, diagnostics, troubleshooting, parts etc.

Roy-c · 01-16-2021, 08:19 AM

You already have the sending unit. Change it and see if it solves the problem. It is not an on / off switch for a gauge but rather a variable resistance to ground which is calibrated to the gauge.

reosw · 01-17-2021, 07:51 AM

SilverLeaf always reads 55 psi just like the idiot gauge. 2003 ISL 400 I have a switch, not a sensor. It read 0 ohms with no pressure so as I suspected it is operating the opposite of what one would think and perhaps the "gauge" is doing the same, which would explain why it was pegging. In other world, sufficient oil pressure opens the switch. Very counterintuitive.

reosw · 01-17-2021, 07:58 AM

With all due respect, it is a switch and reads 0 ohms with no pressure. (The new unit) Lowflyer1 posted a pic of switches vs senders/sensors. Since it reads 0 ohms under no pressure, the only thing that could happen, if it were a sender, the resistance would increase with pressure, ergo, the gauge would have to work opposite. At any rate, I am certain it is simply an on/off pressure switch that is N/C, and opens under pressure.

reosw · 01-17-2021, 07:59 AM

Also, the link doesnt work, but I can google the correct one. I have the Quickserve app on my phone.

reosw · 01-17-2021, 08:01 AM

Can you share the pic of the sender/switch image with Roy-c...he seems to think I have a sender.

mackwrench · 01-17-2021, 08:16 AM

Are you certain your looking at the correct sensor?
Cummins used a oil pressure "switch" that when engine is cranking, tells ECM oil psi is present and engine starts. On most this switch is mounted on side of block, near starter. It doesn't supply any information to the gauge, only tells ECM weather or not oil psi is there.

The oil psi gauge sensor for dash gauge is usually mounted near oil filter head.... sometimes it's supplied by chassis mfg.

I'd suggest putting your engine s/n in quickserve on a PC, quickserve doesn't seem to put everything on the app that's viewable on a laptop, and there's a "as built" diagram showing all sensors/switch locations.