P2B2D: Engine Coolant Temperature Sensor 5 Circuit Low

A low signal from coolant sensor 5 means its NTC resistance has collapsed, which the engine computer would read as an impossibly hot engine; a grounded signal wire or a shorted element is the usual reason. GM documents P2B2D in its configurable temperature input system: the sensor 5 channel fails when its resistance drops below 47.5 Ω in the 2019 L3B tables or 55 Ω in the 2025 ECM tables, a value tied to roughly 150 °C, for 5 s within a 6 s window; Type B, MIL on the second trip. GM bulletin 21-NA-149 lists P2B2D among the codes that chafed engine harnesses produce on 2019–2021 Silverado and Sierra 1500 trucks. NTN-SNR calls it signal too low for sensor 5. Fans may run at full speed until repair. P2B2E is the reverse fault.

Medium severity. Can I keep driving?Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

Symptoms

MIL after two trips
Radiator fans running constantly at high speed
Other harness-related codes stored at the same time

Most likely causes

Signal wire grounded, for example by a chafed harness
Shorted sensor 5 element
Engine control module input fault

What to check, in order

Start with the simplest. You can tick off each step.

With the engine cold, check the coolant level; never do this when the system is hot
With the connector unplugged, check whether the signal wire is making contact with ground.
Check the actual temperature in live data
Make sure the fan comes on when it should
Check the thermostat and connector
Measure the sensor and replace it if its readings do not make sense

Good to know

Repair difficulty: easy
It affects emissions.

What each character of P2B2D means

P: Powertrain: engine and transmission
2: Generic code: same on every make
B: Subsystem depends on the code range
2D: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2B2D?

Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

What causes code P2B2D?

The most common causes are: signal wire grounded, for example by a chafed harness; shorted sensor 5 element; engine control module input fault.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.