P20BF

Code

Generic P — Powertrain

Reductant Heater B Control Circuit Low

Brand: Generic

Type: P — Powertrain

Views: UK: 23 EN: 41 RU: 32

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Verify battery voltage is within normal range (12–14.5 V) with key on/engine off
Inspect fuses and relays related to reductant/heater circuit
Visually inspect connectors and wiring for corrosion, damage, or disconnection
Measure heater element resistance at the heater harness (with connector disconnected)
Check for continuity and short-to-ground or short-to-power from harness to PCM

Supply voltage to heater when command active: approx. battery voltage (~11–14.5 V)
Control output type: PCM low-side switch or PWM ground driver (varies by vehicle)
Expected heater element resistance (typical range): 1–10 Ω (manufacturer-specific)
Expected current draw when active: typically 0.5–15 A depending on element and system
When PCM commands OFF: control line should be open/high (no ground path); when ON: control line should be pulled to ground or show PWM switching

Read and record all DTCs and freeze frame data. Note battery voltage and freeze frame conditions.
Perform a visual inspection of reductant tank area, heater connectors, wiring harness routing, and ground points for corrosion, damage, or water intrusion.
Verify related fuses and relays are good. Replace if blown or intermittent.
With connector disconnected, measure heater element resistance between heater power and ground terminals. Compare to specification; very high or open = failed heater.
Check for supply voltage at the harness fused feed with key ON. No supply = open feed, fuse, or relay fault.
Check control side from PCM: with harness connected, command heater ON via scan tool and measure voltage/current at harness. If PCM commands ON but no ground or PWM present, suspect PCM driver or open between PCM and heater.
Perform continuity checks from harness connector to PCM pin to confirm no open or short. Wiggle wiring to reproduce fault.
If short to ground or power is found, isolate and repair wiring; if open or high resistance at connector, clean/replace connector or harness section.
If heater element is defective, replace heater assembly and retest.
If wiring and heater check good but PCM does not provide correct control signal under command, consider PCM or module-level diagnostics and possible replacement following manufacturer procedures.
Clear codes, perform heater activation tests with scan tool, and verify proper operation and that code does not return during test drive.