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Old 11-07-2012, 08:39 PM
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P2100 OBD code - Intermittent Starting Problems

I have a 2005 Grand Cherokee Limited 5.7 and it's been having intermittent starting problems. When I turn the key, the starter cranks but the engine won't start. I'll be there 5-10min just trying until it finally gives in and starts. It's very random, sometimes 5x a day, other days once or twice, and other days no problems. Crazy thing is, when it does finally start, it runs PERFECT! I had AutoZone test my battery (its good), it can't be the starter because it does crank normally and eventually it does start. When it doesnt want to start I do get a code with the code scanner (P2100 - electronic throttle control motor circuit) I dont get any lights/codes when the truck is on. I really dont have a clue what it could be and everything I thought could've been the problem, I checked and ruled it out. I think that OBD code can be a clue. Anybody have any ideas? Has anyone had this problem?
THANKS EVERYBODY IN ADVANCE!

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Old 01-07-2017, 04:40 PM
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Re: P2100 OBD code - Intermittent Starting Problems

I have recently had the same problem with my 2005 WK 5.7. When it throws the P2100 code, I hold the throttle pedal down about 1/4 inch and hit the starter and it starts. It will rev to about 3000 rpm though, but settles right in to idle rpm. The service manual (Volume 3, page 9-884) has a detailed troubleshooting procedure that includes checking the throttle plate for ice or other obstruction, low battery voltage, and various open and short circuits between the control circuit from the pedal, PCM, and throttle valve assembly. The one common thing in all of the procedures is to 'use a scan tool and select the ETC (Electronic Throttle Control) RELEARN function'. This is something only the dealer will have.
I cleared my P2100 code and placed a mirror on the radiator support and began the start sequence. From the drivers seat, when I have the ignition switch in the run position, my throttle plate flutters a few times, opens about 1/4 inch, then closes to about 1/8 inch opening. Upon start, the throttle plate immediately closes up almost entirely, allowing enough air for idle operation.
There is a throttle position feedback circuit like a lot of vehicles have, and the service manual covers how to check for sweep voltage, closed throttle plate voltages, etc.
Sorry I can't provide more useful information at this time. Like your vehicle, once mine starts, it runs perfectly. If the no-start situation persists, I will have to look into it further. Just not in the cold weather. As long as the partial throttle position works when I hit the starter, I plan on doing that until warmer weather arrives.
I know this response is to an old post. But the information here may help someone to get by temporarily.
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Old 02-04-2017, 01:01 PM
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Re: P2100 OBD code - Intermittent Starting Problems

Greetings All,
I have an update to my post that I would like to share with you since my last reply to this thread.
I had a no-start problem that persisted for two weeks starting about 5 weeks ago. It was always random. Sometimes the no-start would occur before going to work after sitting all night, and at other times after several successful start/re-start cycles during errand running. After 6 unsuccessful attempts in Lowe's parking lot over the course of 15 minutes, I thought I would check for any stored DTC's. There has never been a check engine light displayed with any of the no-start events.The EVIC showed DTC,s P0688 and P2100 (again).
Several years ago, I visited Jeep Grand Cherokee WK - Diagnostic Trouble Codes and printed off the mostly complete list of 2005 WK DTC's. I keep them in the vehicle for emergency reference. In Lowe's parking lot, I remembered the DTC codes list and took a look at it. P0688 showed ASR circuit low voltage, and P2100 (not on the codes list) Electronic Throttle Control Motor Circuit. I didn't have a clue what P0688 was until I got home, after my Jeep finally started.
P0688 ASR is the Automatic Shutdown Relay. It is located in the aft PDC. Upon opening the PDC cover, it is nearest the drivers fender, next to the identical HVAC relay. I removed the ASR relay and 3 blades had a light coating of a white/gray colored powder (corrosion). The fourth blade had a thin coating of a black powdery coating. I carefully cleaned all 4 blades with scotchbrite, removed the HVAC relay and put the ASR relay in its place. I cleaned up the HVAC relay pins and put it in the ASR slot. I then decided to check everything else in the aft PDC. All the other relays had bright, shiny blades-they looked like they were freshly tinned with solder. I carefully removed and checked all identical relays and put them back, but not where they were originally placed.
The battery feeds fuse 6 (50 amp). Fuse 6 feeds the ASR pin 86 which comes out ASR pin 85 and ends up at PCM C3 pin 3 through Connector 104. Fuse 6 also feeds ASR pin 30. When the ASR relay is energized by the PCM, ASR pin 30 is connected to ASR pin 87. Pin 87 feeds fuses 16 and 28 in the PDC, both 25 amp. Fuse 16 feeds the front control module. Fuse 28 feeds to PCM C3, pins 28 and 19, labeled Fused ASD Relay Output.
After checking/cleaning everything in the aft PDC, I opened the front PDC and cleaned every pin on everything in there with scotchbrite. I found fuse pins coated with white/gray powdery material, and brown/tan glaze looking material. I removed all like rated fuses, cleaned them and put them back, but not where they were originally placed.
What a difference! I have not had one incident of no-start in several weeks now. The whole process took me 30 minutes. In my opinion, this should be on everyone's to-do list. My Jeep is now reliable once again. I hated not knowing if it was going to start or not.
The FSM states the P0688 code will reset after 3 successful starts. I wish I had checked for stored codes earlier in the no-start events cycle. There are no stored codes now. After cleaning the PCM and fuse box components, codes P0688 and P2100 have self-cleared.
I hope this helps those of you with random no-start conditions. There is nothing worse than that sinking feeling when your Jeep won't start.
Good luck!
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Old 02-04-2017, 01:47 PM
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Re: P2100 OBD code - Intermittent Starting Problems

Maybe that some di-electric grease on all those previously corroded pins, could prevent corrosion in the future.
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