Won't start. Crank Position Sensor issue? - JeepForum.com
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post #1 of 18 Old 06-07-2021, 12:27 AM Thread Starter
Jeepsmsc2
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Won't start. Crank Position Sensor issue?

2003 WJ 4.0. 191K.

1. Suddenly not starting.
2. Battery is good. Had someone try to jump it.
3. There are no error codes on the odometer
4. If I turn the ignition key, these lights remain light after several seconds: Low fuel light, Engine malfunction light and Sentry Key Indicator.
5. Gas tank should be full. (I don't suspect anyone siphoned the gas out, but haven't rule it out)

Any ideas on probable culprit? Is this the classic Crank Position Sensor failure? Or fuel pump? Loose ground? Other?

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post #2 of 18 Old 06-07-2021, 05:24 AM
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Are you getting a crank with no start?

If so pcm is on the way out, there's endless threads here full of everything you need to research it.

Faulty cps can cause a no start but you'll get a set code for it and the sentry key light staying on is clear indication that the pcm is no longer communicating over the pci bus to the immobilizer module.

The pcm isn't powering up the asd relay, your fuel pump and ignition coils aren't working.
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post #3 of 18 Old 06-07-2021, 07:59 AM Thread Starter
Jeepsmsc2
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Yes It is cranking but won't start.

Is a Mopar PCM recommended or will aftermarket PCM be just fine? If so, any particular aftermarket brand?

Also will the SKI keys work after a plug and play PCM replacement? Or does something special have to be done for SKI keys to work with new PCM? Does it just need a VIN programmed into. the new PCM for the original keys to work with new PCM?
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post #4 of 18 Old 06-07-2021, 11:32 AM
CJ7-Tim
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Diagnostics first before buying parts.

A faulty CPS is the most common cause of random stalling and/or a no-start. CPS failure is common. Most often, a faulty CPS does not trigger the Check Engine Light or store a trouble code.

Test the CPS. Testing is simple and takes less than 15 minutes. If faulty, replace the CPS with a genuine Jeep part only, no Chinese parts.


PCM failure is not very common, but if a new PCM is required, it will need to be married to the SKIM module at the Dealership before being plugged in. Attempting to start a new or used replacement PCM when SKIM is present will lock up the PCM.

“We the people are the rightful masters of both Congress and the Courts,
not to overthrow the Constitution but to overthrow the men who would pervert the Constitution” Abraham Lincoln, 1859.
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post #5 of 18 Old 06-07-2021, 12:17 PM
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Stay far away from remanufactured pcm's, do some research on past threads people keep learning the hard way how bad they are. OEM Mopar is the only way to go and you do not need to get hosed at a dealer junkyards are full of them for cheap that work perfectly every time.

I bench flash pcm's for member's here so it's plug and play ready for you to drop in when it comes back, all you need to do is visit a yard and pull a matching part number pcm out of the same year and drivetrain. There is a part number sticker on the front of the pcm cabinet, for the 2003 4.0 model there are two very different modules available with different part numbers be sure and match them up as the hardware / software flash for early 03 models is not the same as later models couple changes in cooling fan relay and ignition software that year.

Send me a pm with your email if you need help or have questions.
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post #6 of 18 Old 06-08-2021, 11:24 AM
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Quote:
Originally Posted by CJ7-Tim View Post
Diagnostics first before buying parts.

A faulty CPS is the most common cause of random stalling and/or a no-start. CPS failure is common. Most often, a faulty CPS does not trigger the Check Engine Light or store a trouble code.

Test the CPS. Testing is simple and takes less than 15 minutes. If faulty, replace the CPS with a genuine Jeep part only, no Chinese parts.


PCM failure is not very common, but if a new PCM is required, it will need to be married to the SKIM module at the Dealership before being plugged in. Attempting to start a new or used replacement PCM when SKIM is present will lock up the PCM.
Where can I find the CPS test procedure?

I have random stalling and no-start, also no Check Engine Light and the SKIM light turns off properly in the ignition on position.

The starter turns over strong (but doesn't register on the tach) and the battery is good, I tried to start it 4-5 times, let it sit about 45 minutes, tried another 2-3 times, then let it sit overnight and it started right up* this morning.

Last night I was watching CPS swap videos and one kid had three wires shorted in his Cam Position Sensor/Crank Position Sensor portion of the engine wiring harness so when I went out to my car today, I took a volt/ohm meter, unplugged my cam position sensor and did a few continuity checks. Middle pin was ground, outer pins not ground and not shorted. I couldn't see any breaks in the insulation or the harness wrap so I plugged it back in. I did that before trying to start it again, then it started.

I don't know if messing with the cam position sensor did anything or just letting it sit did it.

Looking at my engine harness, it looks pretty good. I wanted to try to check continuity on the crank position sensor connector but it was a longer reach and covered with spilled oil and grime. One thing I wonder about is one plug in the side of the block, pretty much directly above the starter. Its not the starter or a starter solenoid and its not the crank position sensor. It looked OK but I found no mention of it in the ****ty Haynes manual I have (a FSM set has been ordered).

Does any of that narrow down my issues? The previous owner said it was a ground problem.

The only other thing I saw is two wires connected directly to the battery terminals, one positive (with a blade fuse holder) and one negative going to the firewall, down and back somewhere. It doesn't look bad but it's not factory. I have to figure out where they go. I don't see any extra accessories on the car. There is a 12v accessory plug behind the CD changer but I think that is factory. It has a trailer connector by the hitch, maybe that was done after the fact?
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post #7 of 18 Old 06-08-2021, 03:41 PM
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Quote:
Originally Posted by Dust Devil View Post
Where can I find the CPS test procedure?

I have random stalling and no-start, also no Check Engine Light and the SKIM light turns off properly in the ignition on position.

The starter turns over strong (but doesn't register on the tach) and the battery is good, I tried to start it 4-5 times, let it sit about 45 minutes, tried another 2-3 times, then let it sit overnight and it started right up* this morning.

Last night I was watching CPS swap videos and one kid had three wires shorted in his Cam Position Sensor/Crank Position Sensor portion of the engine wiring harness so when I went out to my car today, I took a volt/ohm meter, unplugged my cam position sensor and did a few continuity checks. Middle pin was ground, outer pins not ground and not shorted. I couldn't see any breaks in the insulation or the harness wrap so I plugged it back in. I did that before trying to start it again, then it started.

I don't know if messing with the cam position sensor did anything or just letting it sit did it.

Looking at my engine harness, it looks pretty good. I wanted to try to check continuity on the crank position sensor connector but it was a longer reach and covered with spilled oil and grime. One thing I wonder about is one plug in the side of the block, pretty much directly above the starter. Its not the starter or a starter solenoid and its not the crank position sensor. It looked OK but I found no mention of it in the ****ty Haynes manual I have (a FSM set has been ordered).

Does any of that narrow down my issues? The previous owner said it was a ground problem.

The only other thing I saw is two wires connected directly to the battery terminals, one positive (with a blade fuse holder) and one negative going to the firewall, down and back somewhere. It doesn't look bad but it's not factory. I have to figure out where they go. I don't see any extra accessories on the car. There is a 12v accessory plug behind the CD changer but I think that is factory. It has a trailer connector by the hitch, maybe that was done after the fact?
I believe your PCM is at fault.

2004 Special Edition WJ. LOADED!
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post #8 of 18 Old 06-08-2021, 03:46 PM
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Quote:
Originally Posted by Mattyjm View Post
I believe your PCM is at fault.
Could you elaborate on that?

Can I confirm that with an OBD-2 scan?

How do you rule out other problems?
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post #9 of 18 Old 06-08-2021, 04:57 PM
CJ7-Tim
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Testing and inspection is how to determine the root cause of any problem or faulty parts. Rule out the common and likely, and whatever remains is a primary suspect


Start with the most common and the most likely suspects, the engine sensors, their wire plugs, and their wire harnesses. If the PCM cannot see the data a sensor is producing it is not smart enough to determine if the sensor is faulty, or if the wiring is faulty, it just sees the lack of data, or bad data.

If you are going to throw random new parts at an undiagnosed fault, a handful of genuine Jeep OBD engine sensors is cheaper than a new PCM/ECU/ECM.


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. Typical CPS lifespan is about 150-200,000 miles.

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

Typical CPS Symptoms, (not all symptoms may be present, or occur at the same time) -
- Random stalling
- Starter cranks and cranks but engine won't start up
- Fuel gauge and voltage gauges may not work or display properly.
- You sometimes will have NoBus displayed on the odometer after 30-60 seconds.
- A failed CPS/CKP may or may not throw a CEL trouble code.
- Fuel pump should run and prime for 3-5 seconds.
- No spark at the spark plugs.

When the ignition key is first turned ON, 12 volts travels from the ignition switch to the ASD relay. The PCM provides ground to the ASD relay to energize it. The ASD relay sends the 12 volts to the primary side of the coil. If after a few seconds no signal is detected from the faulty CPS, the PCM opens the ASD relay and 12 volts power to the coil and fuel pump is removed.


If the CPS/CKP is failed sometimes the OBD-II code reader cannot make a connection to the computer or cannot read Check Engine Light/MIL codes because the CPS/CKP has failed.

Diagnostic steps to help 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, 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 these relays as the cause of the no-start. Confirm that the fuel pump 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 lose communication.
-Check the ground connection for the PCM. Make sure it is clean, snug, and has no corrosion.


CPS TESTING PROCEDURE 4.0L H.O. engines
1. Near the rear of fuel rail, disconnect sensor pigtail harness connector from main wiring harness.
2. Place an ohmmeter across terminals B and C or 2 and 3. Ohmmeter should be set to the 10K-or-2OK scale for this test.
3. The meter reading should be open (infinite resistance). Replace sensor if a low resistance is indicated.



If you buy a new CPS, get a genuine Jeep CPS. Most auto parts stores sell cheap crappy Chinese "Lifetime Warranty" parts that are poorly manufactured from inferior materials and are often out of specification, or even failed, right out of the box. The ones that aren’t faulty often 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 simply with genuine Jeep repair parts. Buy good quality repair parts and genuine Jeep sensors for best results.

You must also perform 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 and replace as needed. Do the same for the grounding wires from the battery and engine to the Cherokee's frame/body. Jeeps do not tolerate low voltage or poor grounds and the ECM/ECU will behave oddly until you remedy this.

“We the people are the rightful masters of both Congress and the Courts,
not to overthrow the Constitution but to overthrow the men who would pervert the Constitution” Abraham Lincoln, 1859.
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post #10 of 18 Old 06-09-2021, 12:01 AM
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Some real good info from CJ7-Tim and just to expand on what he is saying.....

There's a ground write up in my signature and look at the 4th photo/diagram in the below link.

https://www.jeepforum.com/forum/f310.../#post39199282

There are 2 grounds for the PCM and they're both on the G103 bolt location which is to the rear of the motor mount on the passenger-side 4.0 engine block just above the oil pan. It's easiest to clean that ground from underneath with the body jacked up behind the passenger-side front tire with the front axle down.

Note that the black/light-blue ground wire coming out of the PCM (C1 connector, #4) is the ground for all engine compartment sensors, all oxygen sensors and the transmission solenoid. That's an awful lot of electronics to connect together with splices coming out of just one ground on the PCM.

From what I've seen a bad G103 PCM ground on either the black/tan or black/white wire can result in a bad ground from the PCM. Often the crank sensor is the first sensor to falter or fail with a bad ground from the PCM plus the PCM itself can become damaged w/o a good ground. I do know that Waterluvr knows his PCM's.

Below is a diagram for testing the crank sensor with an ohm meter and it's the same thing CJ7-Tim posted but in diagram form. Any resistance at all between the power & ground cavities on the sensor connector and the crank sensor is bad. I'd also only use a Mopar crank sensor if you end up replacing it.

Be sure and check pins/receptacles in your cam sensor connector so they're making good contact with the wires. Just mentioning this since it started after you disconnected this cam sensor connector then re-connected it then it started. Good luck.

Here's the crank sensor test diagram.
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post #11 of 18 Old 06-09-2021, 01:36 AM Thread Starter
Jeepsmsc2
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waterluvr was right. the SKI light staying on is a lead indicator of PCM failure.

It was diagnosed that my PCM was bad. A reman part fixed all the problems. I'm still on the original stock CPS. Hope that hangs in there! Looks like a hassle to replace (tight quarters).

I replaced the PCM with a reman Mopar part due to the bad rep of the Chinese stuff. Only option for Mopar now is used / boneyard or remanufactured. Apparently there is no new old stock Mopar PCM left.
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post #12 of 18 Old 06-10-2021, 02:37 AM
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Quote:
Originally Posted by Uniblurb View Post
There's a ground write up in my signature and look at the 4th photo/diagram in the below link.

https://www.jeepforum.com/forum/f310.../#post39199282

There are 2 grounds for the PCM and they're both on the G103 bolt location which is to the rear of the motor mount on the passenger-side 4.0 engine block just above the oil pan. It's easiest to clean that ground from underneath with the body jacked up behind the passenger-side front tire with the front axle down.

Note that the black/light-blue ground wire coming out of the PCM (C1 connector, #4) is the ground for all engine compartment sensors, all oxygen sensors and the transmission solenoid. That's an awful lot of electronics to connect together with splices coming out of just one ground on the PCM.

From what I've seen a bad G103 PCM ground on either the black/tan or black/white wire can result in a bad ground from the PCM. Often the crank sensor is the first sensor to falter or fail with a bad ground from the PCM plus the PCM itself can become damaged w/o a good ground. I do know that Waterluvr knows his PCM's.
Thanks, I'm reading all this on a tablet and it is hard to keep everything straight when half or more is about the 4.7.

I'll check G103 again but I remember wiggling it and it feeling solid. There was no excessive oxidation I could see, it seemed fine.

I wonder if I can test resistance between G103 at the block and pins in the plugs that go to the PCM?

I am really tempted to change the crank position sensor now. I was looking to see where I could find the best deal on an OEM sensor but I can't even definitively find out which part number is right for a 1999. One place says 4897321AA but another says that is for a 2001 I think. Maybe that's the interchange for 1999 but it's not mentioned anywhere that I could find...
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post #13 of 18 Old 06-11-2021, 12:22 AM
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Quote:
Originally Posted by Dust Devil View Post
Thanks, I'm reading all this on a tablet and it is hard to keep everything straight when half or more is about the 4.7.

I'll check G103 again but I remember wiggling it and it feeling solid. There was no excessive oxidation I could see, it seemed fine.

I wonder if I can test resistance between G103 at the block and pins in the plugs that go to the PCM?

I am really tempted to change the crank position sensor now. I was looking to see where I could find the best deal on an OEM sensor but I can't even definitively find out which part number is right for a 1999. One place says 4897321AA but another says that is for a 2001 I think. Maybe that's the interchange for 1999 but it's not mentioned anywhere that I could find...
If you're talking about my WJ ground-write up I tried my best to include the 4.0 with the 4.7 yet keep them separate when need be. Like in this thread I was aiming at the 4.0 and reason I mentioned the 4th photo/diagram in my previous link which is indeed for the 4.0 and G103 PCM ground.

Just because a ground is tight doesn't mean it's making good contact. Often it's difficult to see corrosion or oil directly under the ground eyelets when they're clamped down. Even if it may not be causing an immediate problem I believe it's good preventative maintenance to clean grounds before you have a problem.

Yes, you can check the G103 PCM ground wires resistance using a meter. Make sure you disconnect both the ground and positive cables on the battery before probing any disconnected PCM connector. There are both hot and ground wires in the C1 PCM connector you don't want to cross with your meter probes.

On your 99 4.0 the black/tan PCM ground wire on G103 connects to #32 pin of the large black C1 PCM connector. The black/white G103 PCM ground wire connects to #31 of the same black C1 PCM connector. With this large C1 connector disconnected if you look directly at the connector face #32 will be the far top right pin/receptical while #31 should be just to the left of it. You should see numbering at the ends of the connector rows themselves.

Just to let you know the wiring for the crank sensor is also in the C1 black PCM connector as follows:
#4 crank sensor ground, black/light-blue wire
#8 crank sensor signal, gray/black wire
#17 crank & cam sensor 5V supply, orange wire
(above info from 99 FSM, p.8W-80-81)

Per the 99 WJ official parts list OE 4897321AA is the correct number for the 4.0 crankshaft position sensor. This is the same number you already have and it fits various 4.0 years/models.

Both Rockauto and Amazon sell that Mopar 4897321 crank sensor for just about $100.

Believe I'd be testing the crank sensor for resistance plus cleaning the G103 ground before paying that price or replacing it.

You can also check prices with vendor Kolak on here while below is a good post by Chris Hager from the FAQ's if you do happen to replace the crank sensor on the 4.0. Good luck.

https://www.jeepforum.com/forum/f310...ement-2313281/

PS. Good deal Jeepsmsc2 on fixing your problem.

2004 4.7L WJ Limited, 96 4.0 ZJ


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post #14 of 18 Old 06-11-2021, 09:21 AM
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Thanks, I'm going to get out the volt meter today to check my grounds and the 5v supply.

If that all looks good, I'm probably going to order a new crank sensor.

One more question, my car has never had the CEL come on, will it have any stored OBD-2 codes?

I've been wanting to get an Autel but haven't pulled the trigger yet. I hope I can get an auto parts store to let me borrow a scanner to check it.
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post #15 of 18 Old 06-11-2021, 09:31 AM
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Where did you get the Mopar reman unit? I didnt think there were any Mopar sources for these any more?

'00LMTD-4.7l,242hd,D30,D44A,3.73's,True-trac front,Spartan rear,4" short arm lift,JK'sW/32's
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