Speedo showing incorrect speed - JeepForum.com
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post #1 of 22 Old 02-21-2020, 10:37 PM Thread Starter
G0ldt00th10WJ
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Speedo showing incorrect speed

Got a JGC last week, the speedo is showing speeds that are 5-10 miles per hour over actual speeds. I used my phone with a speedometer and compared the two. When I drove, I can actually see the fuel gauge needle move due to fuel consumption. Can someone help me with this? Idk if the fuel economy is related to the speedo, but it's racking up the miles quite quickly.

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post #2 of 22 Old 02-21-2020, 10:58 PM
Bigrigr
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Your Pic above shows a stock WJ? Are you still running stock sized tires? The number one thing that will throw off the speedo is the tires being the wrong size. If your tires are oversized, it can also effect the fuel consumption.

'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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post #3 of 22 Old 02-22-2020, 08:39 AM Thread Starter
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Originally Posted by Bigrigr View Post
Your Pic above shows a stock WJ? Are you still running stock sized tires? The number one thing that will throw off the speedo is the tires being the wrong size. If your tires are oversized, it can also effect the fuel consumption.


Yes, still running stock tires. I have my GPS mph app showing 35 miles of travel but the speedometer shows 50.1 miles. I don't want to mod anything, just want make it a decent running machine. The suspension is factory, High Country.
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post #4 of 22 Old 02-22-2020, 09:47 AM
WestKy
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Mine did the same thing never did figure it out, 100% stock, even the stock radio clock ran fast. My fix was to buy a heads up GPS display - after 5 years it's going to the junkyard.
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post #5 of 22 Old 02-22-2020, 03:39 PM
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That's a new one on me, and to have two of you with the same issue......at least you both know your not alone in this...Its about gotta be a PCM/BCM issue, maybe the incoming signals run into a traffic jam on the BUS and get scrambled. Just Brainstorming....

'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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post #6 of 22 Old 02-24-2020, 06:07 PM
Scodavvyy
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Same Issue

I picked up my 04 WJ today and immediately noticed that the speedometer was over reading.

It shows 25mph when stationary and is consistently 25mph over all the way up to 80mph(as fast as I've gone in it so far). Was planning to check sensor and cable first and move on from there.

Will update if i figure it out.
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post #7 of 22 Old 02-24-2020, 08:50 PM
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Wow, thats another crazy issue....I gotta believe its the speedometer itself. Almost sounds like the speedo needle is installed incorrectly...

'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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post #8 of 22 Old 02-24-2020, 09:19 PM
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Quote:
Originally Posted by Scodavvyy View Post
I picked up my 04 WJ today and immediately noticed that the speedometer was over reading.

It shows 25mph when stationary and is consistently 25mph over all the way up to 80mph(as fast as I've gone in it so far). Was planning to check sensor and cable first and move on from there.

Will update if i figure it out.
Does it ever read 0?
Have you done the cluster diagnostic, hold the trip button in and turn on the key. Does the speedo do a full sweep?
Maybe the needle is just not on the zero position.
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post #9 of 22 Old 02-25-2020, 05:14 AM
WestKy
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Mine was consistently high by about 15% across the board, ie 30=35mph and 55=64mph. I opted for the GPS mph display over the OBD2 mph display thinking the error was in the computer and the obd2 would have also been wrong. The fact that I was racking up 150 miles for every 100 miles driven didn't bother me as I was gonna drive it into the ground anyways.

I was told to take the Jeep into a dealer to have them flash the ECU but the only authorized place around here is a slaughterhouse.
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post #10 of 22 Old 02-25-2020, 09:26 AM
Scodavvyy
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Originally Posted by Darnice View Post
Does it ever read 0?
Have you done the cluster diagnostic, hold the trip button in and turn on the key. Does the speedo do a full sweep?
Maybe the needle is just not on the zero position.
Will give this a try when my wife brings it home from work. I think it goes to 0 when you turn the ignition off but I'm not sure when the ignition is on, I just know it shows 25mph when the engine is idling and the vehicle is stationary.
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post #11 of 22 Old 02-25-2020, 10:07 AM Thread Starter
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The only thing I can think of is if the previous owner ran larger tires and changed out the speedo gear in the transmission and put factory tires back on and didn't change the gear back to the factory supplied gear.
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post #12 of 22 Old 02-25-2020, 10:33 AM
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I don't believe there is a "speedo gear" in the transmission. After my lift I had to use a Superchips Flashpaq to adjust the reading due to the larger tires.
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post #13 of 22 Old 02-25-2020, 04:50 PM
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Originally Posted by Scodavvyy View Post
Will give this a try when my wife brings it home from work. I think it goes to 0 when you turn the ignition off but I'm not sure when the ignition is on, I just know it shows 25mph when the engine is idling and the vehicle is stationary.
It shows 0 when the ignition is off and 25 mph when the ignition is on but the engine is not running. I ran the gauge diagnostic and the Speedo needle goes all the way to the far end and then returns to bounce of the 10 mph, move up to the 20 mph and then more slowly move to the 25 mph. So i guess its the needles at rest position that i need to adjust.
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post #14 of 22 Old 02-25-2020, 05:39 PM
WestKy
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Does your trip/odometer measure a true mile?
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post #15 of 22 Old 02-25-2020, 06:46 PM
Scodavvyy
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Does your trip/odometer measure a true mile?
It is going up but whether its a true mile I don't know. I'll add that to my list of things to check
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