Check engine light with code U034B after recall for battery replacement and software update 2021 Big Bend

[Susanne Smith]

Ever since the recall for a new battery and software update on our 2021 Bronco Sport Big Bend, we have been getting check engine light with code U034B popping up. Took it to dealer and they could not identify any problem. This issue seems to only be happening after going over bumpy areas (i.e. railroad tracks, rumble strips, etc.) Vehicle went into limp mode one time and after about 20 minutes was able to restart and limp mode was gone. Anyone else had this type of problem and/or been able to resolve the issue. Thank You

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[jkernitzki]

Could just be a loose battery terminal connection. That it happened after a battery replacement and only occurs when encountering bumps lends me to think that's the most likely cause. The U034B can be triggered by bad connections even though it's not directly pointing to the source fault.

 

[Susanne Smith]

Could just be a loose battery terminal connection. That it happened after a battery replacement and only occurs when encountering bumps lends me to think that's the most likely cause. The U034B can be triggered by bad connections even though it's not directly pointing to the source fault.

 

[Susanne Smith]

I had a suspicion that this might be a problem so made sure all of the battery connections were tight. U034B popped up again. Could it possibly be a bad ground connection in the AWD module? Thanks for your response.

 

[jkernitzki]

I had a suspicion that this might be a problem so made sure all of the battery connections were tight. U034B popped up again. Could it possibly be a bad ground connection in the AWD module? Thanks for your response.

I’d have the battery tested. I know it’s new, but that’s no guarantee of performance. Could also be an internal defect in manufacture.

Bad grounds seem to also be a recurring theme.

 

[Susanne Smith]

Could just be a loose battery terminal connection. That it happened after a battery replacement and only occurs when encountering bumps lends me to think that's the most likely cause. The U034B can be triggered by bad connections even though it's not directly pointing to the source fault.

 

[Susanne Smith]

After a diagnostic and battery test, battery tested good and diagnostic, tech says they think problem is gone, but drive it over the weekend and see. Well, first a warning square and bells saying service transmission but no cel. Next day, same warning with cel. Dtc's exactly the same as before, all U codes. New deep dive diagnostic and battery test. Dealer inform us that intermittent short found in PCM, visible water damage. Needs replacement to the tune of $2,000. Wish us luck. To be done on Tuesday.

 

[RSH]

You already received an answer from the dealer of what the issue is.
Here is a list of associated codes.

These codes are commonly diagnosed with error code U034B. As your initial code did not contain any details

• P1624 [2] SBDS Interactive Codes

Sub-Codes From Detailed OBD Scanners

Sub-Code	General Meaning	Possible Causes	Diagnostic Steps
U034B-00 / U034B00	No Failure Details	N/A	No further information.
U034B-01 / U034B01	Short to Battery Voltage	Wiring harness shorted to battery voltage, faulty component, damaged connector.	Inspect wiring for shorts to power, check connectors for damage, test component functionality.
U034B-02 / U034B02	Short to Ground	Wiring harness shorted to ground, damaged component, faulty insulation.	Inspect wiring for shorts to ground, check component grounds, repair damaged insulation.
U034B-03 / U034B03	Low Voltage	Weak battery, poor charging system, voltage drop due to resistance in wiring.	Test battery voltage, inspect alternator output, check for voltage drops in wiring.
U034B-04 / U034B04	Open Circuit	Broken wire, disconnected connector, failed component.	Inspect wiring for breaks, ensure all connectors are properly seated, test component continuity.
U034B-05 / U034B05	Short Circuit Between Wires	Insulation damage causing wires to touch, incorrect wiring repairs.	Inspect wiring harness for damage, repair or replace faulty wiring.
U034B-06 / U034B06	Short to Positive (Other than Battery)	Wiring shorted to another positive voltage source.	Trace wiring to identify unintended voltage sources, isolate and repair wiring.
U034B-07 / U034B07	Short to Negative	Wiring shorted to negative terminal or ground.	Inspect wiring for contact with ground points, repair insulation.
U034B-08 / U034B08	Component Fault	Defective component, internal failure.	Test component operation, replace if necessary.
U034B-09 / U034B09	Sensor Fault	Faulty sensor, sensor out of range.	Test sensor readings, compare to specifications, replace if faulty.
U034B-0A / U034B0A	Circuit Intermittent	Loose connections, intermittent wiring faults.	Inspect connectors and wiring for intermittent issues, perform wiggle test.
U034B-0B / U034B0B	Circuit Voltage High	Overcharging system, faulty voltage regulator.	Test system voltage levels, inspect voltage regulator and alternator.
U034B-0C / U034B0C	Circuit Voltage Low	Undercharging system, excessive voltage drop.	Check battery health, inspect charging system, test for voltage drops.
U034B-0D / U034B0D	High Resistance	Corroded connectors, damaged wiring, loose connections.	Inspect and clean connectors, check wiring resistance, tighten any loose connections.
U034B-0E / U034B0E	Low Resistance	Shorted wires, internal component short, contamination causing short.	Inspect wiring for shorts, test component resistance, clean any contaminants.
U034B-0F / U034B0F	Communication Error	Faulty communication bus, unresponsive module, wiring issues.	Check communication bus integrity, verify module operation, inspect wiring and connectors.
U034B-10 / U034B10	Invalid Data Received	Faulty sensor sending incorrect data, software glitch, interference.	Test sensor output, update/reflash software, check for electrical interference.
U034B-11 / U034B11	Ground Fault	Poor grounding, corroded ground connections.	Inspect ground connections, clean and secure as necessary.
U034B-12 / U034B12	Control Module Fault	Defective control module, internal errors.	Perform module self-test, reprogram or replace module if faulty.
U034B-13 / U034B13	Sensor Not Calibrated	Sensor installation without calibration, sensor drift.	Calibrate the sensor per manufacturer guidelines, replace if calibration fails.
U034B-14 / U034B14	Component Not Programmed	New component requires programming, software mismatch.	Program the component using appropriate diagnostic equipment.
U034B-15 / U034B15	Calibration Error	Incorrect calibration data, corrupted calibration files.	Recalibrate system, update software if necessary.
U034B-16 / U034B16	Incorrect Component Installed	Wrong part number, incompatible component.	Verify part numbers, replace with correct component.
U034B-17 / U034B17	Power Supply Error	Interruption in power supply, fuse blown, relay failure.	Check fuses and relays, test for proper voltage supply.
U034B-18 / U034B18	Overcurrent Condition	Short circuit causing high current, faulty component drawing excessive current.	Inspect for shorts, measure current draw, replace faulty components.
U034B-19 / U034B19	Data Bus Error	Faulty communication lines, bus contention, module malfunction.	Inspect bus wiring, check for conflicting modules, use oscilloscope for signal integrity.
U034B-1A / U034B1A	Redundant Sensor Error	Discrepancy between primary and secondary sensors.	Compare sensor outputs, replace faulty sensor.
U034B-1B / U034B1B	Mechanical Failure Detected	Physical damage, wear and tear, mechanical obstruction.	Perform visual inspection, test mechanical components, repair or replace as needed.
U034B-1C / U034B1C	Actuator Malfunction	Faulty actuator, stuck mechanism.	Test actuator operation, inspect for mechanical binding, replace if necessary.
U034B-1D / U034B1D	Signal Implausible	Sensor signal out of expected range, faulty readings.	Verify sensor signals, compare with known good values, replace sensor if faulty.
U034B-1E / U034B1E	Thermistor Error	Faulty temperature sensor, wiring issues.	Test thermistor resistance, inspect wiring, replace if defective.
U034B-1F / U034B1F	Configuration Error	Incorrect settings, software configuration mismatch.	Check configuration settings, update software, reconfigure as per specifications.

 

[Susanne Smith]

Thank You for this information Robert. When I found out where the PCM is located on the 21 Big Bend, I am surprised that this isn't a large problem for many owners of this model.

 

[Dude]

Thank You for this information Robert. When I found out where the PCM is located on the 21 Big Bend, I am surprised that this isn't a large problem for many owners of this model.

You may be referring to the control module located on the drivers side front fender area above the wheel well liner

the modules located there along with several connectors can experience water intrusion especially when submerged under water for a long enough period of time

I would guess your 2021 experienced water intrusion sometime in its lifetime

https://www.broncosportforum.com/forum/threads/battery-charging-problem-2-293.2189/post-40595

 

[Susanne Smith]

Yes, that is where the module is located. Vehicle has never been submerged in any way, but we do live in Western Washington close to the Cascades. The saying is, 'we don't tan, we rust.'

 

[Dude]

Yes, that is where the module is located. Vehicle has never been submerged in any way, but we do live in Western Washington close to the Cascades. The saying is, 'we don't tan, we rust.'

One of the threads on this forum for a 2021 like yours stated the connectors on that module were damaged by moisture - vehicle was only a couple months old and never in any water - the post stated was a factory issue

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