Powertrain, generic (extended)

P20C2 Reductant Heater C Control Circuit Performance

Check engine lightOn

EmissionsRelevant

Drive cycleRequired

Limp modePossible

P20C2 says heater C is connected but does not take the power the control unit expects. In GM's 2025 tables heater 3, the second tank heater, must measure between 1.50 and 2.60 ohms and stay within 29 W of its command; otherwise Type A after 8 s. Ford reads the code differently on its diesels: there it means the heater supply voltage has dropped below 5 V, tested a single time per trip with the heaters at full load and again within the glow plug module diagnostics, so a weak feed or relay is the first suspect. FCA titles it Reductant Heater 3 Control Circuit Performance on the 3.0 L EcoDiesel and issued several PCM reflashes against false entries, among them 18-028-14 and 18-019-15. Deutz lists it for the return line heater as over-temperature. The usual result is late dosing in frost.

Likely causes

Heater supply below 5 V because of a weak relay, fuse or feed wire (Ford)

Engine control software setting the code falsely (FCA 18-028-14, 18-019-15)

Heater C element resistance outside its window

Symptoms

Check engine light after a heating cycle
DEF thaws slowly in cold weather
Further heater codes if the common supply is weak

Repair estimate

DifficultyMediumWorkshop job

Parts and labour€0–1,200

Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

reductant line heater c

References: gsi.ext.gm.com, fordservicecontent.com, static.nhtsa.gov, static.nhtsa.gov.