P2B77: Coolant Heater B Control Circuit Low
Methodology: We combine code standards with complaint and reliability patterns, then review for clear, vehicle-first diagnosis steps.
Sources: SAE/OBD-II definitions, manufacturer service information, and public reliability reports (including NHTSA where applicable).
Limits: Guidance is informational and may not match every model-year or revision. Confirm with the official manual and diagnostics before replacing parts. For safety-critical or electrical work, use a qualified technician.
What Does P2B77 Mean?
P2B77 is a diagnostic trouble code indicating: Coolant Heater B Control Circuit Low. This code relates to the vehicle systems system. The vehicle's computer detected a condition outside normal operating parameters and stored this code.
Symptoms of P2B77
- ⚠️ Check Engine Light (MIL) illuminated
- ⚠️ Coolant Heater B reading at zero or minimum value
- ⚠️ Related system not functioning or in fail-safe mode
- ⚠️ System warning light illuminated
Common Causes
- 🔍 Open or broken wire in Coolant Heater B circuit
- 🔍 Poor ground connection at Coolant Heater B
- 🔍 Faulty Coolant Heater B with no output signal
- 🔍 Disconnected or loose Coolant Heater B connector
- 🔍 Blown fuse in related circuit
Frequently Asked Questions
What does P2B77 mean?
Can I drive with code P2B77?
How much does it cost to fix P2B77?
What To Do Next
Possible Fixes
- 🔧 Repair broken wire or restore ground in Coolant Heater B circuit
- 🔧 Clean and secure Coolant Heater B connector and ground points
- 🔧 Replace failed Coolant Heater B
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1
Find your vehicle above
Click your make and model for real owner reports and common causes specific to your vehicle.
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2
Check for recalls
Go to nhtsa.gov/recalls and enter your VIN. Free repairs if covered.
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Get a professional diagnosis
A code alone doesn't identify the exact failed part. A diagnostic ($50–$150) pinpoints the root cause.