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U0616 Lost Communication With Engine Coolant Bypass Valve B

Check engine lightOn

EmissionsRelevant

Drive cycleNot required

Limp modeNo

Valve B is a second electronically controlled coolant valve, for example one that splits flow between the block and the head or toward a heater or oil cooler; which valve carries the letter B depends on the manufacturer. No manufacturer documents U0616 publicly. The code means the controller has stopped receiving valid replies from that valve over its digital link, while valve A may still answer, so the fault is likely in the branch of wiring, the connector or the electronics of valve B itself. Suppliers such as Hella and Rheinmetall build these valves with LIN, PWM or SENT interfaces and internal position feedback. CARB requires a monitoring plan for engines that regulate temperature with more than one flow control device. P0E7B to P0E7E cover the electrical circuit of valve B.

Likely causes

Damaged signal, supply or ground wire in the branch to valve B

Loose, corroded or wet connector at valve B

Electronics in valve B failed

Controller software or configuration does not match the fitted valve

Symptoms

Warning lamp, often without a noticeable change in driving
Unusual warm-up behaviour or coolant temperature swings

Repair estimate

DifficultyMediumDIY possible

Parts and labour€30–700

Time0.5–2.5 h

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

Parts involved

coolant bypass valve bvehicle bus wiring

References: law.cornell.edu, rheinmetall.com, hella.com.