U3020 Control Module Wake-up Circuit B High

U3020 sets when wake-up line B stays above its valid level, typically through contact with a battery or ignition feed, or because its source holds it on. The practical effect differs from U301F: a permanently active B line keeps asking the module to stay awake even when line A and the bus have gone quiet, so the module cannot enter sleep and the 12 V battery runs down while parked. Ford's 2019 hybrid OBD summary shows how much a high wake level can trigger, since its battery module starts contactor checks whenever the charge wake-up is high. At the same time a transceiver such as NXP's TJA1043 only wakes on a level change, so the fixed high line cannot pass on a real request from source B. No manufacturer documents U3020 publicly. A parasitic draw test with the line unplugged confirms the cause.

Likely causes

Symptoms

• 12 V battery flat after parking
• Module stays awake with the vehicle locked

Repair estimate

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

Parts involved

Related codes

References: nxp.com, fordservicecontent.com, law.cornell.edu.