P20B4 code meaning
Reductant Heater Coolant Control Valve Circuit High
Powertrain system Generic code P20xx codes Check engine light
What P20B4 means
P20B4 is the opposite electrical case to P20B3: the drive circuit of the reductant heater coolant valve reads too high, which points to a short to battery voltage on the control line or, with certain driver designs, an interrupted ground return. The control unit can then no longer switch the valve, and the heating loop stays in whatever position the valve spring holds. On coolant-heated installations, such as Bosch supply modules supplied with a cooling-water heating option, that decides whether the module thaws at all. No manufacturer documents P20B4 publicly; CARB's comprehensive component rules form the basis. Measure with the valve connected, because some controllers cut the output after a fault, as Hino describes for its valve.
P20B4 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 2.5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P20B4
- Malfunction indicator and SCR warning on
- Valve cannot be actuated in an output test
- Slow DEF thaw in winter
Common causes of P20B4
- Most likelyValve control wire shorted to battery voltage
- PossibleOpen ground return of the valve circuit
- Less likelyOutput stage in the control unit defective
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Reductant coolant valve
What each part of P20B4 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 0 | Area: fuel and air metering and auxiliary emission controls. |
| B4 | The exact fault in that area. |
What to do next
- Note P20B4 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P20B4
What does P20B4 mean?
P20B4 means "Reductant Heater Coolant Control Valve Circuit High". P20B4 is the opposite electrical case to P20B3: the drive circuit of the reductant heater coolant valve reads too high, which points to a short to battery voltage on the control line or, with certain driver designs, an interrupted ground return. It is a generic code, so it means the same on every make.
Is it safe to drive with P20B4?
Drive gently and only to a workshop. With P20B4 the car can go into limp mode (reduced power) to protect itself.
Will P20B4 fail an emissions test?
Yes, it can. P20B4 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P20B4 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2.5 hours of work. This is a job for a workshop.
Will P20B4 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.