ⓘ Information only. This page provides general educational information about fault code P138B. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P138B mean?
P138B is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Glow Plug Control Module System Voltage.
Manufacturer-specific notes
Some manufacturers publish additional definitions or variations for this code. Always cross-check with your vehicle's own service documentation.
About Glow Plugs codes
Glow plug codes appear only on diesel engines. Glow plugs heat the cylinders before cold starts; a failed plug or relay typically shows up first as harder cold starting in winter, then as a stored code as the system detects the open circuit.
P138B is one of 98 codes in this category. Browse all Glow Plugs codes →
What we know about P138B specifically
We record the SAE J2012 standardised definition and the system this code belongs to, but we have not yet published detailed driver-reported symptoms, common causes, or step-by-step diagnostic guidance for P138B.
Rather than invent that information by generating generic content from a template, we leave it out. For specific guidance, the most reliable sources are:
- •your vehicle's own service manual or manufacturer-specific technical bulletins
- •a qualified mechanic with a manufacturer-level diagnostic tool
- •a marque specialist familiar with your make and model
Codes nearby
Codes adjacent to P138B in the P-code series. Many fault codes appear together with their neighbours because they relate to the same circuit or component.
Other Glow Plugs codes
Other fault codes in the same system as P138B. The ones with detailed guides have plain-English explanations, symptoms, causes, and diagnostic steps.
Spotted an issue or have something to add? Mechanics, technicians, and drivers who have first-hand experience with P138B can submit a correction or expansion. We review every submission before publishing, mechanic submissions are prioritised.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →