U0680 Code Symptoms, Causes, Diagnosis & Repair Overview Guide

U0680 Code Symptoms, Causes, and How to Fix Them

Drivers first notice the problem when the check‑engine light illuminates and the vehicle’s performance feels off. Rough or uneven idle, a sudden drop in miles‑per‑gallon, and occasional stalling—especially when climbing a hill or descending rapidly—are common complaints. Because the barometric sensor tells the PCM how air density changes with altitude, any loss of that data forces the engine to run on default fuel‑trim values, which produces the symptoms listed above.

Symptoms

• Check‑engine (MIL) illumination – the PCM stores the U0680 code and flashes the warning lamp.
• Rough idle – engine speed wavers between 600‑900 rpm, sometimes shaking the steering wheel.
• Reduced fuel efficiency – fuel‑trim calculations revert to a safe, rich setting, raising consumption by 5‑15 %.
• Stalling during rapid elevation changes – loss of altitude data causes the PCM to mis‑adjust fuel, leading to momentary shut‑off.
• Inaccurate altitude‑related fuel‑trim readings – live data on a scan tool shows “Barometric Pressure Sensor B – No Signal.”

If any of these signs appear together, the vehicle’s PCM is no longer receiving pressure data from Sensor B.

Why This Happens

Faulty Barometric Pressure Sensor B

The sensor itself can fail electrically or mechanically. Internal diaphragm rupture or a shorted output circuit prevents the sensor from sending a voltage signal to the PCM.

Wiring Harness Damage or Connector Corrosion

The sensor’s signal travels through a dedicated wire bundle and a connector at the PCM. Frayed wires, broken pins, or corrosion from moisture can interrupt the communication path, triggering U0680.

Power‑train Control Module Internal Fault or Software Glitch

Even with a healthy sensor and wiring, the PCM may suffer a failed communication controller, damaged micro‑controller pins, or corrupted firmware that blocks the sensor’s data stream.

Ground or Power‑Supply Issues

A poor ground strap or a voltage drop on the PCM’s supply rail can cause intermittent loss of sensor data, especially under load when the engine is climbing a steep grade.

Environmental Factors (Extreme Temperature or Moisture)

Severe cold can make the sensor’s output sluggish, while water ingress into the connector can short the signal line. Both conditions are more likely to produce intermittent U0680 events.

Diagnostic and Repair Procedures

1. Read the freeze‑frame data – use a professional scan tool to pull the U0680 code and any accompanying sensor values. Verify that the barometric pressure reading is “N/A” while other sensors (MAP, MAF, O₂) are normal.
2. Perform a live‑data test of Sensor B – locate the sensor (typically on the intake manifold or HVAC housing) and measure its voltage with a multimeter while the engine is running. A healthy sensor should produce a steady 0.5‑4.5 V signal that varies with altitude.
3. Inspect wiring and connectors – trace the sensor’s harness from the sensor to the PCM. Look for cracked insulation, exposed conductors, or water intrusion. Clean the connector pins with electrical contact cleaner and reseat them firmly.
4. Check PCM power and ground – measure voltage at the PCM’s supply pins (usually 12 V) and ground resistance (should be < 0.1 Ω). Replace any corroded ground straps.
5. Reset the code and perform a functional test – after any wiring or sensor repair, clear the code and drive the vehicle through an elevation change (e.g., a short hill). Monitor for re‑appearance of U0680.
6. Re‑program the PCM – if the sensor and wiring are sound but the code returns, update the PCM’s software to the latest manufacturer version. Many manufacturers release communication‑module patches that resolve intermittent sensor‑loss issues.
7. Consider PCM replacement – when re‑programming does not eliminate the fault and the PCM shows internal communication failure (e.g., no response to any sensor), replacement is the most reliable solution.

Typical labor for the complete diagnostic sequence ranges from $120‑$180, while a PCM re‑programming session adds $80‑$120.

When Replacement Makes More Sense

A PCM that repeatedly loses communication with Sensor B after wiring repairs and software updates is likely suffering from internal hardware degradation. Continued attempts at repair can become costly and may not restore long‑term reliability. In such cases, a fresh, VIN‑matched PCM eliminates the risk of recurring faults and restores full power‑train functionality.

Modern control modules are complex and integrated with security, immobilizer and emissions systems. That’s why choosing a replacement isn’t only about the hardware—correct programming and VIN‑specific calibration are essential. Flagship One specializes in VIN‑matched control modules, providing a plug‑and‑drive solution backed by a comprehensive warranty. Their modules arrive pre‑programmed to the vehicle’s exact specifications, ensuring seamless integration and eliminating dealer‑only re‑coding delays.

Preventive Maintenance

• Inspect sensor wiring annually – especially after winter service, check for cracked insulation and moisture at the connector.
• Keep the sensor and connector clean – remove debris and apply a dielectric grease to the pins to guard against corrosion.
• Verify PCM power and ground integrity – a loose ground strap can develop over time; tighten or replace it during routine service.
• Update PCM software promptly – manufacturers issue communication‑module updates that address known sensor‑loss bugs; schedule these updates during regular service intervals.
• Avoid prolonged exposure to extreme moisture – if the vehicle is stored in a damp environment, use a breathable cover and check the sensor area for condensation before driving.