Jeep Enthusiast Forums banner

P1391 after replacing crank position sensor

174K views 28 replies 16 participants last post by  jetnjeff29r 
#1 ·
Hey guys (n gals)..new member here with a problem. I'm trying to fix a friends 2001 cherokee classic. He was having cylinder misfires and multiple cylinder misfires, occasionally the car would shake badly on idle. a new coil pack was fitted, new plugs, oil change, new idle sensor.
He just got back from a 200 mile drive and complained that when he got there the a/c wasn't working (blowing warm air i think) the car was very lumpy at idle, and when it stalled would not restart until 1 hour later. i checked the OBD and it had a multiple cylinder misfire code and cylinder 1 & 3 misfire codes.
I just got replaced (20 mins ago) the crank position sensor and now there is a P1391 code and it feels like the engine is misfiring or something, when it had misfire codes before the engine idled very nicely ( except for the few lumpy occasions)..I don't get it...any idea what could be going on.
 
#2 ·
What is an idle sensor ? Do you mean the Idle Air Controller, sometimes called an idle stepper motor ?

P1391 (M) Intermittent Loss of CMP or CKP Loss of the Cam Position Sensor or Crank Position sensor has occurred.

Where did you buy the Crank Position Sensor ? Is it installed correctly ? Most auto parts stores sell cheap crappy Chinese "Lifetime Warranty" parts that are poorly manufactured, often out of specification, or even failed, right out of the box. Many times they have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured with genuine Jeep repair parts. Cheap parts are cheap for a reason.

Reboot the ECU/PCM engine computer using the instructions below.

This very simple procedure will Erase the "Adaptive Memory" stored inside the PCM and allow a new "Adaptive Memory" to be developed.
After performing this procedure the PCM will re-learn and store into Adaptive Memory your engines performance characteristics.
Perform these steps exactly as they are written, in the order they are written. This will cause the adaptive memory in the PCM to be erased and cause the PCM to go into Fast Learn Mode adaptive mode. Disconnect the POSITIVE battery Terminal and touch it to ground ( not the battery negative terminal ) for 30 seconds. The engine block or the A/C compressor pump will work as a ground. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory.

Reconnect the Battery Cable
Turn Ignition Switch to the "On" position but DO NOT start the engine
Turn Headlight "On"
Turn Headlights "Off"
Turn Ignition Key "Off"

The PCM Adaptive memory has now been flashed, or erased from the PCM. When you start the engine it will be running off a set of pre-programmed tables that come with the PCM from the factory. When you get the engine up to operating temperature the PCM will start to collect data for the "Adaptive Memory". The PCM will collect data for Adaptive Memory for the first 50 Warm-up Cycles.
 
#3 ·
yes i did mean the idle air controller.
Crankshaft position sensor bought new on ebay..yes, installed correctly.

I just asked my bud about the "new" misfire, and he said it was doing that on his journey. Was not doing it when i drove it a few days ago.

I just had a friend over who suggested disconnecting the camshaft position sensor (to run closed loop) and the misfire went away, reconnecting the sensor bought back the misfire.

Does this look like another bad sensor?...or should i do the system reprog you suggested Tim?

Is it true i need a special tool to align the camshaft sensor if i replace it?
Thanks for the fast reply
 
#4 · (Edited)
..... suggested disconnecting the camshaft position sensor (to run closed loop) and the misfire went away, reconnecting the sensor bought back the misfire.

Does this look like another bad sensor?...
The system re-boot is free and causes no harm.

By disconnecting the camshaft position sensor and having the misfire go away, one might assume that the cam sensor or the related wiring has issues. I would replace it. Just install a new one, no calibration or alignment needed.
 
#5 ·
Thanks Tim, that puts my mind at rest, advance will have one for me in the morning $59. I'll have a few threads i imagine. The vehicle was recently purchased and not in the condition the seller stated :+(
I'm happy to do the work as i learn as i go...i'm finding my way around Jags in the same forum manner.
I appreciate your help and as i get to know my way around will be contributing to threads.
I'll do the re-boot after i replace the sensor (tomorrow)...(almost today!)
 
#6 ·
so this morning i go out to pick up the sensor and the jeep won't start, turns over fine, sounds like no spark or no fuel. i pressed the schrader valve on the fuel rail, a little pressurised gas came out, tried to turn the engine over again and re-checked the shrader (no pressure tester here) again a little pressurized fuel, so i'm assuming fuel is getting to the rail. is it possible or probable that the camshaft sensor is causing this no-start?...coincidently the day after changing the crank sensor...i know a crank sensor can cause a no start, checked the crank sensor connector, checked and di-electric-ed the camshaft sensor electrical connector.
Advance auto failed to actually order the camshaft sensor, so it'll be a few day wait. I did the system re-boot...no difference, tried starting the vehicle with the camshaft sensor disconnected...no difference....now stumped
 
#8 · (Edited)
...........new sensor lasted a whole 15 miles!
As you have just discovered, cheap automotive parts are cheap for a good reason. Most auto parts stores sell cheap crappy Chinese made parts, some that even come with a "Lifetime Warranty". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that are not faulty many times will have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep engine sensors. Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep repair parts.

If you want good parts that will fit right, work right, and last, you need to buy brand name parts. I always get genuine JEEP parts and have never been disappointed.

.
 
#14 ·
I've been working on XJs for a long time and the crankshaft position sensor is one part that I always purchase from the Jeep dealer.

Yes, it does cost more. But it will also last longer than (most) aftermarket parts and as it is a critical sensor that can leave you stranded, it is money well spent.
 
#16 ·
When changing topics, it is best to start your 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.

.

.
 
  • Like
Reactions: Rottidog
#17 ·
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.
 
#19 ·
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.
 
#20 ·
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. Next, test the sensors for proper function.
 
#25 ·
Solved!!

First time posting.
Had the same problems (CPS and CPK Codes) rough idle or no start. Read posts, here and other forums. Was going to re-replace (distributor style) Cam Position sensor but decided to garb hold of the tone spinney thingy that the sensor senses. (Don’t do this while it’s spinning). I thought to myself “Hmmm that’s odd…. this spinney thing rotates freely. This is supposed to be, directly, geared to the oil pump / crankshaft” I then decided to pull it out….”Clink clank clunk” The small gear that was on the Cam position sensor shaft dropped into the oil pan.

The spring pin that holds the gear to the Cam position sensor shaft had sheared off. Once I got the gear out of the oil pan and replaced the whole assembly the engine worked fine.

Hope this helps.
 
#27 ·
Yes, it will cause your jeep to die as you're going down the road. I was going about 65 mph and lost ALL power, put it in nuetral and start her right up. I bought a new crankshaft sensor from the Jeep dealership yesterday for $117. I took out the old one and put in the new one last night. Not sure if the swap fixed my problem yet but just writing to explain how difficult it was to get the old one out and put the new one in. That sensor is way up in there. I needed a two foot long extension, a swivel socket connector, and a 7/16 socket (I think an 11mm works as well). Another tip, take out the small bracket that holds the wiring for the crankshaft sensor and the oxygen sensor out of the way. That made it much easier to get the long extension up in there. Getting the new one in was very difficult for me. Off to reset the PCM. Good luck.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top