P1391 after replacing crank position sensor - Page 2 - JeepForum.com
Search  
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > Models > Jeep Cherokee & Comanche Forums > XJ Cherokee Technical Forum > P1391 after replacing crank position sensor

Brand New! Quadratec LED Headlights!FS: Wrangler RGB Multicolor Fog Light LEDs: Awesome EffectFS: 2007-2013 Jeep Wrangler "HALO" Angel Eye Kit

Reply
Unread 08-23-2010, 01:08 PM   #16
CJ7-Tim
Real Jeeps have dents.
 
CJ7-Tim's Avatar
2000 XJ Cherokee 
 
Join Date: Apr 2002
Location: out in the garage - Minneapolis, Minnesota
Posts: 21,481
When changing topics, it is best to start you own thread.



The most likely cause of it cranks and cranks but won't start up is the Crankshaft Position Sensor (CPS) located on the transmission bell housing. Often this part is also referred to as the CranKshaft Position Sensor (CKP) CPS/CKP failure is very common. The CPS/CKP can stop working with no warning or symptoms and the engine will not run or the engine may randomly stall for no apparent reason.

Crank Position Sensors can have intermittent “thermal failure”. This means that the CPS/CKP fails when the engine gets hot, but works again (and will test as “good”) when it cools back down.

Begin with basic trouble shooting of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Do the same for the grounding wires from the starter to engine block, and from the battery and engine to the Jeep's frame/body. Jeeps do not tolerate low voltage or poor grounds and the ECM/ECU may behave oddly until you remedy this.



Symptoms –
- Starter cranks and cranks but engine won't start up and run.
- Fuel gauge and voltage gauge may not work or display properly.
- You sometimes will have No Bus on the odometer after 30-60 seconds.
- A failed CPS/CKP may or may not throw a CEL trouble code.
- No spark at the spark plugs.
- Fuel pump should run and prime for 3-5 seconds.

If the CPS/CKP is failed sometimes the OBD-II trouble code reader cannot make a connection to the ECU/computer or cannot read Check Engine Light/MIL codes because the CPS/CKP has failed. Disconnect the code reader, disconnect the CPS/CKP wire connector, and reconnect the code reader. If the code reader establishes contact with the ECU and scans, your CPS/CKP is failed and needs to be replaced.


Diagnostic steps to confirm the CPS is the cause of your no-start


You should be able to verify a bad cps, by unplugging it, and turning the ignition key to on. If the voltage gauge and/or the fuel gauge now displays correctly and/or the No-Bus is gone, replace the CPS.

Unplugging and reconnecting the CPS sensor where it connect to the main harness near the back of the intake manifold usually resets the ECU and if the jeep fires right up after doing this you can bet that the CPS is faulty and needs to be replaced.

Exchange the fuel pump relay and the ASD relay with one of the other similar ones in the PDC to eliminate the relays as the cause of the no-start. Check the ASD relay fuse.

Confirm that the fuel pump to runs for 3-5 seconds when you turn the ignition key to ON.

Eliminate the NSS as a cause of no start. Wiggle the shift lever at the same time you try to start. Put the transmission in Neutral and do the same. Do the reverse lights come on when the shifter is in Reverse?

Inspect the wires and wire connectors at the O2 sensors on the exhausts pipe. A short circuit from melted insulation or from broken O2 sensor wires can blow a fuse and the ECU/ECM will loose communication. Don’t get tunnel vision and assume the sensor is bad (unless it tests bad with a meter). Damaged wiring or a dirty connector can inhibit the signal from making it to the computer. Inspect/test/clean/repair wiring or connectors as necessary.


CPS Testing


Crankshaft Position Sensor Connector (CPS/CKP)



.



TESTING PROCEDURE 1991 – 2001 4.0L H.O. engines

1. Near the rear of intake manifold, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C (See Image). Ohmmeter should be set to 1K-to-1OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.

TESTING PROCECURE for 1987 – 1990 4.0 L engines

Test # 1 - Get a volt/ohm meter and set it to read 0 - 500 ohms. Unplug the CPS and measure across the CPS connector's A & B leads. Your meter should show a CPS resistance of between 125 – 275 Ohms. . If the CPS is out of that range by much, replace it.

Test # 2 - You'll need a helper for this one. Set the volt/ohm meter to read 0 - 5 AC volts or the closest AC Volts scale your meter has to this range. Measure across the CPS leads for voltage generated as your helper cranks the engine. (The engine can't fire up without the CPS connected but watch for moving parts just the same!) The meter should show .5 - .8 VAC when cranking. (That's between 1/2 and 1 volt AC.) If it's below .5vac, replace it.


The 2000 and 2001 will have the CPS in the same location on the bell housing, but the wire connector may be on the passenger side, not as shown in the diagram below. Simply follow the wire from the sensor to the connector.

.
If this information has been helpful, please click on the "thumbs up" icon on the bottom right side of this section.

.

.

__________________
.

According to the National Shooting Sports Foundation, AR-15 sporting rifles account for nearly 20% of all U.S. firearms sales.

Progressive Liberalism: Bringing you new Healthcare ideas so wonderful, they have to include mandatory participation ......

Originally Posted by Ronald W. Reagan: Government is not the solution to our problem; Government is the problem.
CJ7-Tim is offline   Reply With Quote
Unread 08-23-2010, 01:16 PM   #17
GCJoe
Registered User
2001 XJ Cherokee 
 
Join Date: Jul 2007
Location: Simpsonville, SC
Posts: 170
Thanks for the large amount of info Tim. That should get me started nicely. I thought my question was someone related to the discussion but next time I won't be lazy and will start my own thread. My apologies to the OP.
__________________
GCJoe
2001 XJ
Bone Stock
GCJoe is offline   Reply With Quote
Unread 08-25-2010, 02:13 PM   #18
95jy
Registered User
1995 YJ Wrangler 
 
Join Date: May 2009
Location: illinois
Posts: 166
Thanks guys good info
95jy is offline   Reply With Quote
Unread 12-21-2012, 06:38 PM   #19
BobEyler
Registered User
 
Join Date: Dec 2012
Location: Proctor, West Virginia
Posts: 1
Hi, 2001 PT Cruiser here. I found this forum. Pretty much everything everyone else has done was done to try to get the P1391 Code to clear. I finally found the problem to be the wiring harness that runs around the back of the engine. The wire tie broke and let the harness drop and run the axle. The harness has a mesh sleeve over in. When sitting in the garage jacked up, the harness was a couple of inches away from the axle. It must have dropped when driving the car. It missed very badly under load. When I pulled the harness down to look for problems, it rolled over and I didn't see that one of the crank position sensor wires was worn in two. I pulled the harness up out from behind the motor and spliced the wire back together. It now has two layers of split loom taped around it and 10 wire ties holding it in position. It runs great again.

For everyone that has had the P1391 Code, I feel your pain. It has been raining for days here and every time I took it out and found it still wasnt fixed, then pulled back into the garage to work on it and crawled under the car, it dripped on me making it harder to find the problem. I was a couple of hours away from setting the car on fire and pushing it over the hill.
BobEyler is offline   Reply With Quote
Unread 12-22-2012, 08:00 AM   #20
CJ7-Tim
Real Jeeps have dents.
 
CJ7-Tim's Avatar
2000 XJ Cherokee 
 
Join Date: Apr 2002
Location: out in the garage - Minneapolis, Minnesota
Posts: 21,481
While the OBD diagnostics system and the P trouble codes are helpful for narrowing ones search for problems, having specific codes does not always equal having a specific failure. If the ECU engine computer cannot see data from a sensor, it reacts the same as if the sensor itself has failed.

A wise troubleshooter should always start with the simple, cheap, and obvious solutions and then work their up to more complex fault possibilities. First you should always inspect the wires, and wire plugs to the systems/sensor covered by trouble codes. As suggested, look for chafed or melted wire insulation, corrosion, missing/bent pins in the wire plugs, and damaged or pinched wires.
__________________
.

According to the National Shooting Sports Foundation, AR-15 sporting rifles account for nearly 20% of all U.S. firearms sales.

Progressive Liberalism: Bringing you new Healthcare ideas so wonderful, they have to include mandatory participation ......

Originally Posted by Ronald W. Reagan: Government is not the solution to our problem; Government is the problem.
CJ7-Tim is offline   Reply With Quote
Unread 12-22-2012, 09:31 AM   #21
OnTheFence
Registered User
 
Join Date: Oct 2012
Location: USA, USA
Posts: 434
Yet another "DO NOT BUY SENSORS AFTERMARKET"
DEALER ONLY
OnTheFence is offline   Reply With Quote
Unread 12-22-2012, 10:15 AM   #22
tsc
Registered User
2006 LJ Wrangler 
 
Join Date: Mar 2007
Location: Pacific Northwest
Posts: 514
the one reason I carry a space in my glove box in the last 15 years these have left me stranded 2 or 3 times..

Gotten pretty good at replacing them too.
tsc is offline   Reply With Quote
Unread 12-23-2012, 09:08 AM   #23
Kevin108
Registered User
2000 XJ Cherokee 
 
Join Date: Aug 2009
Location: Portsmouth, VA
Posts: 3,784
My aftermarket sensors have been fine but I still carry spare CPS and CKP in the toolbox.
__________________
My build thread has pics again. http://www.jeepforum.com/forum/f177/kevin108s-2000-xj-build-867428/
Kevin108 is online now   Reply With Quote
Unread 03-11-2014, 10:56 PM   #24
Ospina01
Registered User
1997 XJ Cherokee 
 
Join Date: Aug 2013
Location: Orange, California
Posts: 3
I know this is an old thread but im just now having a problem...... so

Tim, thank you for all your help and your detailed info
Ospina01 is offline   Reply With Quote
Reply

Tags
cam position , ckp , cps , crank position , p1391
Thread Tools


Suggested Threads





Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.