OBD-II Diagnostic Trouble Code
U0168 — Lost Communication With Vehicle Security Control Module
U0168 means modules lost communication with the vehicle security control module, which runs theft deterrent and alarm functions and on some vehicles shares immobilizer duties. Its messages stopped arriving within the allowed time. How this module relates to the immobilizer depends on the manufacturer.
Severity 3/5
Truck-relevant
Service this week
Severity
Service this week
Lost Communication With Vehicle Security Control Module
Code
U0168
Category
Network
Subsystem
Network
Truck-relevant
Yes
What this means for truckers
U0168 (Lost Communication With Security Module) — security/immobilizer module offline.
Before you replace parts — try this first
U0168 on the Network system is most often low battery voltage — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
A security or theft light may stay on or flash, the alarm may act on its own, and on some vehicles the engine will not start or will start and stall. Remote locking may not work.
Common causes
- CommonLow battery voltage ($100–$700)
- CommonFuse, power or ground problem at the security module ($50–$250)
- OccasionalDamaged wiring or corroded connector ($150–$500)
- RareFailed security control module ($300–$1200)
How to fix
Test the batteries and charging system
When to use: First step
Check power, ground and network circuits to the security module
When to use: When voltage is good
Replace and program the security module, including key relearn if needed
When to use: After the wiring has been verified
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → U0100 — Lost Communication With ECM/PCM A
- → U0101 — Lost Communication With TCM
- → U0102 — Lost Communication With Transfer Case Control Module
- → U0103 — Lost Communication With Gear Shift Module
- → U0104 — Lost Communication With Cruise Control Module
Frequently Asked Questions
Can I drive with code U0168?
U0168 is severity 3 — plan service within a few days. Performance is likely degraded already (you may feel reduced power, harsher shifts, or slightly worse fuel economy). Continuing to drive risks additional damage to adjacent components.
How much does it cost to fix U0168 on a commercial truck?
Total repair cost ranges $50–$1200 depending on the root cause. The cheapest fix is usually the first one listed below — Low battery voltage — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will U0168 fail a DOT inspection?
U0168 is generally not a direct DOT inspection fail item by itself. Inspectors focus on safety-critical systems (brakes, steering, tires, lights, hours-of-service). However, the check engine light alone can trigger additional inspection scrutiny. Best practice: fix the code and clear it before a planned inspection.
What's the difference between U0168 and related codes?
U0168 is closely related to: U0100 (Lost Communication With ECM/PCM A), U0101 (Lost Communication With TCM), U0102 (Lost Communication With Transfer Case Control Module), U0103 (Lost Communication With Gear Shift Module). These codes share the same subsystem (network) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only U0168 is set without the companions, the issue is more isolated.
How do I prevent U0168 from coming back after a repair?
For U0168 (Lost Communication With Vehicle Security Control Module), prevention centers on the network system. Pay attention to ground connections at every PM — bad grounds are 70% of communication codes. Inspect harness routing for chafe points. Don't disconnect modules with the key on.