U351B code meaning
High Voltage System Interlock Circuit D Low
Network system Generic code U35xx codes Check engine light
What U351B means
U351B reports that too little level comes back from interlock loop D while the module drives it. GM's hybrid tables for the loop A code P0A0C give a frame of reference: the test only runs when on-board voltage exceeds 10.2 V, judges what fraction of a 5 V test signal returns against a 30 % limit and logs a Type A fault after two failed 12.5 ms readings. A weak 12 V battery thus pauses the check instead of tripping it. No maker publishes a calibration for U351B. Typical causes are a wire crushed against the body, a loop plug left off, or a dead source; the contactors behind loop D may not close.
U351B at a glance
- Check engine lightYes, usually on
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor0.5 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U351B
- No ready mode or high-voltage branch D unavailable
- Warning to have the high-voltage system checked
- Fault stays present after clearing until the wiring is repaired
Common causes of U351B
- Most likelyLoop D wire pinched against the body and shorted to ground
- PossiblePlug within loop D not seated after a repair
- Less likelyTest voltage source in the controller failed
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Hvil loop dHvil wiring
What each part of U351B means
| U | Network system: communication between the control modules (CAN bus). |
| 3 | Reserved range, usually generic. |
| 1B | The exact fault in that area. |
What to do next
- Note U351B and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U351B
What does U351B mean?
U351B means "High Voltage System Interlock Circuit D Low". U351B reports that too little level comes back from interlock loop D while the module drives it. It is a generic code, so it means the same on every make.
Is it safe to drive with U351B?
Drive gently and only to a workshop. With U351B the car can go into limp mode (reduced power) to protect itself.
Will U351B fail an emissions test?
U351B is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U351B to fix?
Difficulty: hard. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will U351B clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.