Service trailer brake system warning displays when nothing is connected to truck

U1900 FORD - CAN Communication Bus Fault

Read more: https://www.autocodes.com/u1900_ford.html
Possible causes
Faulty / intermittent ignition switch connections
CAN Bus wiring intermittently open/shorted to power or ground Faulty / intermittent connection at PCM
Faulty electrical connections at ABS Control Module
Faulty electrical connections at the instrument cluster
Poor connections at the trailer brake controller/trailer connector

Tech notes This is typically a false/intermittent code. It can occur if: Someone hooks up a scanner to the OBDII port while the ignition is on or while the engine is idling. A trailer brake system is installed improperly/incorrectly on a truck with ABS (anti-lock brakes).

When is the code detected? When the PCM, Brake Controller and Instrument Cluster are unable to communicate with each other at any time while the ignition switch is turned to the "Run" position, code U1900 sets in memory.

Possible symptoms Engine Light ON (or Service Engine Soon Warning Light) Amber ABS (Anti-lock Brakes) Light ON Wrench Light On

U1900 Ford Description The Anti-ock Brakes System (ABS) module, the Powertrain Control Module (PCM), and the instrument cluster communicate over the Controller Area Network (CAN) Bus. This is a high-speed bus communication system and is not fault tolerant, which means any type of intermittent/loose connection between these 3 controllers will cause communication to stop. When the PCM, ABS module and instrument cluster are unable to communicate with each other at any time while the ignition switch is turned on, code U1900 will set.

Read more: https://www.autocodes.com/u1900_ford.html

SERVICE TRAILER BRAKE SYSTEM
This message will be displayed when there is a problem with the TBCM system. If this message persists over multiple ignition cycles there is problem with the TBCM system. Take your vehicle to an authorized GM dealer to have the TBCM system diagnosed and repaired.

Do you know what DTC'S - diagnostic trouble code's are ?
DTC B3894
DTC C0561
DTC C056D or C056E
DTC C0800
DTC C0845
DTC C0870, C1112, C1113, C1114, or C1119
DTC C0880, C0890, C1115, C1116, C1117, or C1118

Your best bet , take it to a qualified repair shop.

SERVICE BRAKE BOOSTER
Refer to Brake Warning System Description and Operation in Hydraulic Brakes

SERVICE BRAKE BOOSTER
The SERVICE BRAKE BOOSTER message will be displayed when the supplemental brake assist signal circuit is toggled at 1.0 Hz with a 50 percent duty cycle. This message is also displayed if the instrument panel cluster (IPC) does not see an alive and well signal at key on. When this message is displayed it indicates a problem with the SBA and should be serviced or replaced.

How do the power brakes work ? Good .?

Service Brake Booster Message Displayed
Step
Action
Yes
No
Schematic Reference: Brake Warning System Schematics
1
Did you review the Brake Warning System Description and Operation and the Brake Assist System Description and Operation and perform the necessary inspections?
YES - Go to Step 2
NO - Go to Symptoms - Hydraulic Brakes
2
Start the vehicle.
Is the REDUCED BRAKE POWER message displayed for 1 minute before the SERVICE BRAKE BOOSTER message is displayed?
YES - Go to Step 3
NO - Go to Step 4
3
Perform the Brake Assist System Diagnosis
Did you find and correct the condition?
YES - Go to Step 12
NO - Go to Step 11
4
Disconnect the Supplemental Brake Assist connector.
Test the ignition 1 circuit for an open or a short to ground.
Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
YES - Go to Step 12
NO - Go to Step 5
5
Test both ground circuits for opens.
Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
YES - Go to Step 12
NO - Go to Step 6
6
Test the engine on signal circuit for an open or a short to ground.
Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
YES - Go to Step 12
NO - Go to Step 7
7
Test the vehicle speed signal circuit for an open.
Did you find and correct the condittion?
YES - Go to Step 12
NO - Go to Step 8
8
Test the supplemental brake assist signal circuit for an open or a short to voltage.
Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?
YES - Go to Step 12
NO - Go to Step 9
9
Connect the supplement brake assist connector.
Disconnect the instrument panel cluster connector.
Connect a DMM from battery positive voltage to the supplemental brake assist signal circuit.
Turn the ignition to the RUN position while observing the DMM.
Did the DMM flash battery voltage?
YES - Go to Step 11
NO - Go to Step 10
10
Replace the Supplemental Brake Assist pump motor assembly Refer to Power Brake Booster Auxiliary Pump Replacement .
Did you complete the replacement?
YES - Go to Step 12
--
11
Replace the instrument panel cluster. Refer to Instrument Cluster Replacement in Instrument Panel, Gages and Console.
Did you complete the replacement?
YES - Go to Step 12
--
12
Start the engine.
Does the Service Brake Booster message stay on?
Go to Step 2
System OK

by releasing the park brake you are in fact putting air in the park brake (spring brake diaphragms) that compresses the springs and allows the brakes to release. When you apply the park brake you are in effect dumping the air out of the system and allowing the spring brakes to come on. The light is telling you that there is insufficient air in the park brake circuit to fully release the spring brakes. Some ideas are that the air lines on the trailer are opposite to the prime mover(tractor), there is a kink in the air lines in the trailer , the air tank that holds emergency air for the spring brakes system has an internal leak in a valve between chambers or externally between air tanks. I would make very sure that I fixed this problem before I travelled as the consequences of a trailer wheel lock up at speed could have very serious results.

Might help to know what kind of trailer brake controller it is

Possibly a defective ABS sensor, or low brake fluid. Recommend a reputable mechanic to assess the issue.

The Left Turn signal is DARK GREEN/RED
The Right Turn signal is WHITE/YELLOW
The Left Brake light is WHITE/ORANGE
The Right Brake is WHITE/RED
The High-Mount Brake lamp is DARK GREEN/WHITE

Now, with all that said, your Jeep should be already equipped with trailer wiring unless you have the cheapest model of Jeep Liberty available. I would check your Owner's Manual on the subject.

Also, your rear lighting is controlled by the Body Control Module (BCM) and the signal and brake inputs/outputs are all transmitted to the Instrument Cluster Module for your lamp-out warning system. Anything you connect to this wiring can adversely affect BCM function or can cause your lamp out warning to malfunction and come on all the time. I would use extreme caution unless you really want to destroy some HIGH DOLLAR electronics in your vehicle.

RE: check engine light, stop by any good parts store and have an OBII scan (fault scan). That will pull codes that will identify what triggered light. RE: Brake lights, check wiring in and around tail lights (especially if you have trailer wiring)

{: ) SERVICE PARK ASSIST The driver information center (DIC) displays SERVICE PARK ASSIST when the park assist module detects a malfunction in the object detection system and sends a request to the DIC for display of the message. The DIC also displays SERVICE PARK ASSIST when there is a loss of communication with the park assist module.
PARK ASSIST OFF The PARK ASSIST OFF message is displayed in the DIC when the park assist system is disabled due to conditions that disable or inhibit the system. The red LED in the rear display, as well as, the telltale in the switch will be lit, notifying the driver the PARK ASSIST system is disabled. The object alarm module requests the DIC via the serial data circuit to display PARK ASSIST OFF when it detects that one of the following conditions is true:
• The object alarm system is disabled through DIC vehicle customization feature. Refer to the Owners Manual for more information. • An object is attached to the rear of the vehicle, such as a trailer, bicycle rack, or hitch receiver. • An object is hanging out of the endgate. • The park brake is not fully released. • The system receives vibrations from a large nearby vehicle or from a heavy equipment such as a jackhammer. In the case of objects attached to the rear of the vehicle such as a trailer, hitch receiver, or a bicycle rack, or objects hanging out of the endgate, the rear parking assist (RPA) will have an Automatic Object induced disable feature where the RPA will determine if the rear object is moving with the vehicle. If the RPA detects such a condition, the park assist will be disabled. The PARK ASSIST OFF message will continue to be displayed until the trailer hitch receiver is removed and the vehicle is driven forward above 24 km/h (15 mph).