Codes U1110 and U1120, not starting?

Tiny
HLEANN77
  • MEMBER
  • 2018 JEEP LIBERTY RENEGADE
  • 2.4L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 90,000 MILES
Hello. My vehicle listed above had starting issues for a couple of months on and off. Wouldn't start but would when jumped. This past Saturday, however, this no longer worked. Now it will not start at all. We replaced the battery. Nothing. Had a friend come to scan it and codes u1110 and u1120 came up. What could this be and how can we fix it? Really need my vehicle operable. Thank you in advance.
Friday, November 8th, 2024 AT 2:41 PM

3 Replies

Tiny
AL514
  • MECHANIC
  • 4,677 POSTS
Hello, both of these codes have to do with the engine computer (PCM) and its communications with the ABS module. (U1120 Lost Wheel Distance Message) (U1110 Lost Vehicle Speed Message). So, it's possible the ABS module or PCM is affecting the network it's on, such as pulling the network down completely by shorting it to ground or a short to battery power or sending out corrupted message packets.

Does this scan tool have the capability to scan the entire vehicle network? If so, trying to communicate and read codes from the ABS module would be the next step. The PCM is the module setting these codes, but it may be communicating with the scan tool on a different network than what the ABS and PCM communicate on.

In many cases when a network is affected and we can see the network corruption on an oscilloscope, we will go through and unplug some modules to see if the network comes back to a normal waveform. Which is something you could try, with the key Off and out of the vehicle, you can unplug the ABS module connector and see if the vehicle starts,
The ABS looks to have a CAN C1 and a CAN C2 coming in and out of it. Which goes to many other modules in the vehicle. But try reading codes from the ABS module first and going through and checking all fuses.

With this being a no start condition, I think you would find other codes stored in other modules if a full system scan was done. The scan tool being used might be a basic OBD2 scanner that only reads PCM codes, and is not able to scan every module. It might even show that communication with some modules is not possible, which would indicate additional problems.

https://www.2carpros.com/articles/can-scan-controller-area-network-easy

https://www.2carpros.com/articles/anti-lock-system-testing-and-repair-abs

https://www.2carpros.com/articles/how-to-check-a-car-fuse
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Friday, November 8th, 2024 AT 5:32 PM
Tiny
HLEANN77
  • MEMBER
  • 2 POSTS
Would this be why the brake is so hard to push in? It's a push start so you have to press in the brake to start it and the brake is really stiff. Thank you for the answer.
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Saturday, November 9th, 2024 AT 4:26 AM
Tiny
AL514
  • MECHANIC
  • 4,677 POSTS
This is all most likely related, the brake master cylinder and the brake booster (which is what assists you to push on the brake pedal), along with the ABS hydraulic unit and control module are all pretty much integrated together. Plus, if you have been pushing on the brake pedal a bunch of times trying to start the vehicle, the booster will not be working without the engine running, but that should not stop the Brake pedal switch from sending a signal that the pedal is being pressed.
The real issue here is these "U" codes, and any other codes that are stored in other modules throughout the vehicle. Below is a picture of the brake master cylinder, the brake booster which is the large round component that the master cylinder bolts to, and the ABS module.
Is this something you are going to try to diagnose yourself, or have it taken to a shop?
It doesn't necessarily have to be a bad ABS module causing these issues, that's just the only code that a basic scan tool can read because it was stored in the engine computer. To read codes from other modules, like the ABS, a higher end scan tool is needed.
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Saturday, November 9th, 2024 AT 10:54 AM

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