Do you know what a serial data network is ? With all the computers car makers put on thier cars these day's they need a communication network for them to talk ,share info. on etc. U codes are codes for the network . A module could be down ,could be a wiring problem . A shorted module or bus wire can bring down the whole vehicle. Could cause the vehicle not to start ,systems not to function . How did you pull this code ,with what scan tool or code reader ? Did it come from the PCM - engine computer ? Need a up scale professional scan tool to check all module's on the vehicle , need to pin point the module that is causing the problem .
U1900
CAN Communication Bus Fault - Receive Error
4WD Control Module
REPAIR all other DTCs first. CLEAR the DTCs. CYCLE the key OFF then ON and wait 10 seconds. REPEAT the self-test. If DTC U1900 is still present, REFER to Section 418-00 .
U1900
CAN Communication Bus Fault - Receive Error
ABS Module
REPAIR all other DTCs first. CLEAR the DTCs. CYCLE the key OFF then ON and wait 10 seconds. REPEAT the self-test. If DTC U1900 is still present, REFER to Section 418-00 .
U1900
CAN Communication Bus Fault - Receive Error
DSM
REPAIR all other DTCs first. CLEAR the DTCs. CYCLE the key OFF then ON and wait 10 seconds. REPEAT the self-test. If DTC U1900 is still present, REFER to Section 418-00 .
U1900
CAN Communication Bus Fault - Receive Error
Instrument Cluster
REPAIR all other DTCs first. CLEAR the DTCs. CYCLE the key OFF then ON and wait 10 seconds. REPEAT the self-test. If DTC U1900 is still present, REFER to Section 418-00 .
U1900
CAN Communication Bus Fault - Receive Error
Occupant Classification Sensor Module
REPAIR all other DTCs first. CLEAR the DTCs. CYCLE the key OFF then ON and wait 10 seconds. REPEAT the self-test. If DTC U1900 is still present, REFER to Section 418-00 .
U1900
CAN Communication Bus Fault - Receive Error
Parking Aid Module
REPAIR all other DTCs first. CLEAR the DTCs. CYCLE the key OFF then ON and wait 10 seconds. REPEAT the self-test. If DTC U1900 is still present, REFER to Section 418-00 .
U1900
CAN Communication Bus Fault - Receive Error
RCM
REPAIR all other DTCs first. CLEAR the DTCs. CYCLE the key OFF then ON and wait 10 seconds. REPEAT the self-test. If DTC U1900 is still present, REFER to Section 418-00 .
U1900
CAN Communication Bus Fault - Receive Error
Retractable Running Board Module
REPAIR all other DTCs first. CLEAR the DTCs. CYCLE the key OFF then ON and wait 10 seconds. REPEAT the self-test. If DTC U1900 is still present, REFER to Section 418-00 .
016 CAN Communications
SECTION 418-00: Module Communications Network
2007 Explorer/Mountaineer/Explorer Sport Trac Workshop Manual
DESCRIPTION AND OPERATION
Procedure revision date: 08/02/2006
Communications Network
Vehicle communication utilizes both medium and high speed controller area network (CAN) communications. CAN is used for many modules to communicate with each other on a common network. CAN in-vehicle networking, is a method for transferring data among distributed electronic modules via a serial data bus. Without serial networking, intermodule communication requires dedicated, point to point wiring resulting in bulky, expensive, complex, and difficult to install wiring harnesses. Applying a serial data network reduces the number of wires combining the signals on a single network. Information is sent to the individual control modules that control each function.
The vehicle has 2 module communication networks:
- Medium speed (MS) CAN
- High speed (HS) CAN
Both networks are connected to the data link connector (DLC). This makes diagnosis and testing of these systems easier by allowing one scan tool to be able to diagnose and control any module on both networks from one connector. The DLC can be found under the instrument panel between the steering column and the audio unit.
Network Topology
Module Name
Network Type
Termination Module
Anti-lock brake system (ABS) module
HS-CAN
No
Audio control module (ACM)
MS-CAN
No
Digital versatile disc (DVD) player (if equipped)
MS-CAN
No
Driver seat module (DSM) (if equipped)
MS-CAN
No
Electronic automatic temperature control (EATC) module (if equipped)
MS-CAN
No
Four wheel drive (4WD) control module (if equipped)
HS-CAN
No
Instrument cluster (IC) (gateway module)
HS-CAN
MS-CAN
Yes
Yes
Occupant classification sensor (OCS) module
HS-CAN
No
Parking aid module (PAM) (if equipped)
MS-CAN
No
Powertrain control module (PCM)
HS-CAN
Yes
Power running board (PRB) module (if equipped)
MS-CAN
No
Restraints control module (RCM)
HS-CAN
No
Satellite digital audio radio system (SDARS) (if equipped)
MS-CAN
No
Smart junction box (SJB)
MS-CAN
Yes
Transmission control module (TCM) (if equipped)
HS-CAN
No
MS-CAN Network Operation
The MS-CAN network communicates using bussed messages. The MS-CAN has an unshielded twisted pair cable, data bus (+) and data bus (-) circuits. In addition to scan tool communication, this network allows sharing of information between all modules on the network.
The MS-CAN is a medium speed communication network used for the following modules:
- SJB
- Audio unit
- Instrument cluster
- DSM (if equipped)
- DVD player (if equipped)
- EATC module (if equipped)
- Parking aid module (if equipped)
- Satellite audio receiver (if equipped)
- Power running board module (if equipped)
HS-CAN Network Operation
The HS-CAN network communicates using bussed messages. The HS-CAN network uses an unshielded twisted pair cable, data bus (+) and data bus (-) circuits. In addition to scan tool communication, this network allows sharing of information between all modules on the network.
The HS-CAN is a high speed communication network used for the following modules:
- PCM
- TCM (if equipped)
- RCM
- ABS module
- Instrument cluster
- Occupant classification sensor module
- 4WD control module (if equipped)
Network Termination
The CAN network uses a network termination circuit to improve communication reliability. The network termination of the CAN bus takes place inside the termination modules by termination resistors. Termination modules are located at either end of the bus network. As network messages are broadcast in the form of voltage signals, the network voltage signals are stabilized by the termination resistors. Each termination module has a 120 ohm resistor across the positive and negative bus connection in the termination module. With 2 termination modules on each network, and the 120 ohm resistors located in a parallel circuit configuration, the total network impedance, or total resistance is 60 ohms.
Network termination improves bus message reliability by:
- stabilizing bus voltage.
- eliminating electrical interference.
Gateway Module
The instrument cluster is the gateway module, translating HS-CAN to MS-CAN and vice versa. This information allows a message to be distributed throughout both networks. The instrument cluster is the only module on this vehicle that has this ability.