Powertrain, generic (extended)

P20C7 Reductant Heater D Control Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P20C7 reports that heater D's control circuit is grounded or overloaded with current. Only Deutz publishes the code: for its downstream line heater (SPN 520471) it maps to FMI 4, a voltage that is too low or a short to a low source. No vehicle maker documents thresholds for heater D. GM's tables for heaters 1–3 show the usual method, comparing the output voltage with the heater off against a low band and the current with it on, then setting Type A, set after a 2 s window; Ford uses 15 A on its two heater circuits. CARB requires such output circuits to be monitored for shorts that contradict what the module has commanded. Look for chafing on the line harness, water in a connector or an element with an internal short. Open and high counterparts are P20C5 and P20C8, the performance test is P20C6.

Likely causes

Heater D wire chafed through to ground
Water in the heater D connector
Internal short inside the heated downstream line

Symptoms

  • Warning lamp, possibly with a blown fuse
  • Unheated downstream line and delayed dosing in frost

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–800
Time0.5–3 h

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

Parts involved

reductant line heater d

Related codes

P20C5P20C6P20C8P20C3P20BFP20BB

References: serdia.deutz.com, law.cornell.edu, gsi.ext.gm.com.