U1122: Lost Odometer Data on SCP Bus
The U1122 code indicates that a control module has detected a missing or invalid odometer data message on the SCP (Standard Corporate Protocol) communication bus. This Ford-proprietary network, used primarily in 1990s-2000s vehicles, relies on periodic messages between modules. When the receiving module fails to get the odometer message within the expected time or finds a checksum error, it logs this communication fault. Note that this code does not necessarily mean the odometer itself is broken; rather, the data is not being transmitted correctly over the bus.
1. Commonly Affected Makes
2. Most Common Causes
- Faulty instrument cluster (IC) that generates the odometer message
- Open or short circuit in the SCP bus wiring (SCP+ and SCP- circuits)
- SCP bus termination resistor out of specification (typically 120 ohms)
- Body control module (GEM/BCM) with internal communication failure
- Electromagnetic interference corrupting bus messages
- Corroded or damaged pins in the instrument cluster connector
- Faulty receiving module that misinterprets valid messages
3. Symptoms You Will Notice
- Odometer reading may be erratic, blank, or show dashes
- Check Engine Light or other warning lights illuminated
- Other communication-related codes may be present
- Possible issues with other gauges or instrument cluster functions
4. Step-by-Step Diagnosis
Scan for all stored codes and freeze frame data to confirm U1122 and related codes.
Visually inspect the SCP bus wiring and connectors for damage, corrosion, or loose pins, especially at the instrument cluster and BCM.
Measure resistance between SCP+ and SCP- at the DLC (Data Link Connector) – should be approximately 60 ohms (two 120-ohm termination resistors in parallel).
If resistance is out of range, isolate and test each module's termination resistor.
Check for proper voltage on SCP+ (typically 2.5V) and SCP- (typically 2.5V) with the ignition on.
If wiring and termination are good, suspect the instrument cluster or BCM; perform a module communication test or swap known-good modules if possible.
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, the vehicle is generally safe to drive, but the odometer may not display correctly, which can be a legal issue for mileage tracking. The underlying communication fault may also affect other systems. It's recommended to diagnose and repair promptly.
How much does it cost to fix?▼
Costs vary widely: a simple wiring repair might be $100-$200, while replacing an instrument cluster can range from $300 to $800 or more, depending on the vehicle and whether programming is required.