U1146: PATS Communication Failure
Code U1146 indicates that the Powertrain Control Module (PCM) or Body Control Module (BCM/GEM) has detected invalid data or missing expected security messages on the SCP (Standard Corporate Protocol - J1850 VPW) bus. This fault is directly related to the Passive Anti-Theft System (PATS), where communication between the key transceiver module, the instrument cluster (HEC), and the PCM is interrupted or corrupted, preventing verification of the coded key.
1. Commonly Affected Makes
2. Most Common Causes
- Open circuit, short to ground, or short to battery on the SCP bus (+/-) wiring
- Faulty or disconnected PATS transceiver module (antenna ring around ignition cylinder)
- Instrument cluster (HEC) with internal communication failure
- PCM with internal SCP bus driver failure
- Low battery voltage or voltage spikes corrupting network communication
- Corroded, loose, or backed-out terminals in the DLC or involved module connectors
3. Symptoms You Will Notice
- Engine cranks but does not start
- Theft light flashing or staying on solid
- No communication with PATS modules during scan
- Instrument cluster warning lights or erratic behavior
4. Step-by-Step Diagnosis
Verify battery voltage is at least 12.6V and stable; charge or replace if low.
Scan all modules for related codes; check for communication with PCM, BCM, and instrument cluster.
Inspect SCP bus wiring for opens, shorts, or damage; measure resistance and voltage at DLC pins 2 and 10.
Check PATS antenna ring connector and wiring for damage or corrosion.
Test PATS transceiver module by swapping with known good unit if available.
If wiring and modules check out, suspect PCM or instrument cluster internal failure; perform pinpoint tests per service manual.
5. Frequently Asked Questions
Is it safe to drive?▼
No, the vehicle may not start or may stall unexpectedly due to the anti-theft system preventing engine operation. This is a high-severity issue that should be diagnosed and repaired immediately.
How much does it cost to fix?▼
Repair costs vary widely depending on the cause: from $50-$150 for a wiring repair or connector cleaning, to $200-$500 for a PATS antenna ring, $400-$800 for an instrument cluster repair/replacement, or $500-$1,200 for PCM replacement and programming.