trips1

Got CEL and VSC lights on while driving on the Freeway.
On checking the error codes got the numbers P1780 and P1780* which seems to point to PNP switch malfunction (Park/Neutral Position switch). Cleared the error code this morning and at least the CEL did not come up again after 5-6 miles of driving. Will wait to see if it shows up again.

Have few questions to all the helpful people here:
- I did a transmission pan change a week ago before this CEL came up. At that time i had overfilled the transmission oil by about 1/4quart which i removed after a day.
Is there anything i might have messed up in pan/oil change that might mess up the PNP switch?

- If the CEL comes up again i will post here again. But want to check here if there is any kind of risk in driving the car with this CEL on, in case i cannot get to fix it soon.

Thanks again in advance to everyone here.

trips1

CEL and VSC lights came up again :-(
Any suggestions what i should look for to identify if my pan/oil change might have messed some PNP electrical connection or if i should directly go for changing the PNP switch.

salimshah

The error codes only mean that ecu is getting some signal which is not within expected good value for the zone (function).

I can not verify that your error message is due to PNP switch but assuming you have verified that the function is related to PNP or over-drive.

It could be that the switch involved is bad.
Wiring has gone bad between battery-switch-ecu
Ecu has gone bad.

In reality any combination listed above can cause the failure, but likely hood of 2 or more going bad is low.

Proper test procedure is given in the service manual. You can give us your observations from instrument cluster and tail-light. Go through each gear position and list PRND21 bulb lighting up and in R your rev light in the back should light up. You should only be able to start in P or N.

Salim

trips1

Thanks for the information Salim!
Tried what you recommended and here are the observations.
- Reverse gear tail lights on the back are good
- Other than the already not working D light all the other gear indication lights on the panel lights good.
- The car only starts in P and N. It does not start in RD21

Today morning i disconnected the battery for 30 minutes and that has cleared the lights. I guess similar to yesterday the CEL/VSC/TRAC lights will come back up again later in the day.

Please can you point me to the soft copy of the service manual where i can take a look at the complete test procedure.

Thanks,
Trips

salimshah

Due to copyrights we can not link the soft copy here in CL. You can get legal subscription to ALLDATA for day(s)/month(s) etc.

If you search hard enough you may find one on the net.

By your observation PRP switch seems good.

Salim

trips1

Was able to find a 99 service manual online and hopefully that would apply for most part to the 2001 RX too
BTW one of the posts on another forum had an instance reported by someone where they got this same error code because of alternator problem. So i did check my battery as well as its charging by the alternator and that seems to be fine. (12.x volt stationary and then 14.x volt after starting the car.)

Sincere apologies for requesting for more spoon feeding, but unfortunately i have never worked with the ECM module before. The service manual asks for testing voltages at certain wires connected to the ECM. As such i have some questions that i need help with before i start work.

- Once i remove the glove compartment and reach the ECM module how do i get access to the specific wires.
- Where do i connect the ground pin (black) of my multimeter. Is there any specific wire available on ECM for it.
- Need confirmation that i should use multimeter with the DCV setting of 20.
- I crawled under the car but could not figure out where exactly is the PNP switch. Do i need to remove the bottom splash guard and look for PNP switch towards the front adjoining the transmission oil pan?

Since i cannot start the car in R/D/L/2 and also there absolutely no noticeable difference in how the car drives or how the automatic gears shift, would someone have any gut feeling from their experience what might be wrong,

By any chance would folks recommend that i go to an independent mechanic and hand them the printout of the P1780 error code from the service manual and ask them to first check that my ECM is working fine or not.

Thanks,
Trips

maxSteel

Body ground
Use a thin wire to probe into the harness.
Voltage is battery voltage, so a 20 DCV range is fine
Park/Neutral switch location - not sure, but manual says 'remove engine under cover'

trips1

Just thought it fit to update this thread with the current status even though the end result is still a mystery.

- I got under the car to check the PNP switch connectors and everything looked good.

- I was not comfortable playing with the ECU myself and so i went to an independent Lexus specialist. The mechanic cleared the code, checked the ECU and also took the car for a ride with some kind of Toyota diagnostic tool attached and the CEL light did not come up. In absence of any other indicators he suspected that it might have to do something with ECU going bad and asked me to come again if the CEL comes back and he can try to use a replacement ECU temporarily to diagnose it further.

- This time the CEL came back after much more time (say 50-60 miles) than in the past (say 8-10 miles).

- I cleared the CEL once again and it has not come back up even after 1200 miles of driving.

So at this time i am keeping my fingers crossed!

rosen71

P1780 is the PNP switch circuit malfunction. It could be wiring, the switch itself, and the connectors. I would suggest you to change the switch. After that, if the problem is still there, check the connectors. Very often there could be a momentary bad connection, and the Error is in the memory straight away. With excluding the switch as a reason, you can go further.

trips1

I was this Thread Starter
So in last 8 years (since Sept 2015) I got P1780 couple of times and each time after clearing the CEL things worked just fine for 6-8 months.
Now about one month ago I got P1780 once again and this time clearing CEL has not helped. Every time I clear CEL it comes back up again after 10-15 miles.

Since there is no problem in driving the car I would have not worried about this, if it was not for the upcoming Smog check early next year.
Has anyone got their PNP switch/sensor changed and can point me to the part number and comment if I need to go with original Lexus/Toyota for this part? Also if I need to change my ECU, what would be the best route. Look for one in the junk yard from an older car? I saw some being sold on ebay too.
Of if anyone found anything new related to this P1780 PNP switch issue, please share.

trips1

Please can someone let me know if the following part number is correct for PNP switch for 2001 RX300.
84540-06010

And more importantly have someone used the aftermarket part available on Amazon and eBay and has worked fine for them.

Thanks!

salimshah

Please verify the part number with your vehicle vin#. Manufacturer can change part number midstream of a production year as well as how the vehicle is equipped.

If you are reluctant to call your local Lexus parts, please visit on line Lexus parts dealer web site. I think there is one Scottsdale AZ and one in Georgia Atlanta.


Salim

trips1

Even after changing the PNP switch I am still getting the CEL P1780.
Please can someone give additional pointers what should be my next step. There is no issues whatsoever in the actual working of PRD21. I can only start the car in P and N, and can't start in RD21
So it appears all the mechanical parts are good.
Should I look at getting the ECU checked? Does anyone knows how much does it take to get a refurbished ECU for 2001 Lexus RX300? If it is indeed a ECU issue then please can someone let me know if an independent mechanic will be able to help or I need to go to to Lexus dealership?

Thanks!

salimshah

See https://www.clublexus.com/forums/es-...lfunction.html post #3. Not RX forum but I think the controls are similar.

I think there is some confusion about PRND switch and PNP switch.

Lexus or any other mechanic needs proper instrumentation to zero into the defect. Without proper equipment and know how, one resorts to replace and see.

Salim