01 Steering Wheel Feels Loose? Uneven Tire Wear? Don't Ignore … • 02 How to Become a Pilot: A Guide for Aspiring Aviators • 03 Mechanics Say This Common Driving Behavior Causes More Engi… • 04 That Faint Vibration In The Seat Could Be The First Sign Of… • 05 Gearbox Oil Change: When to Do It and Why It's Important • 06 P0420 Code Explained: Catalyst System Efficiency Below Thre… • 07 The Science of Flight: How Aircraft Stay in the Air • 08 People Shocked After Mechanic Explains the Hidden Danger of… • 09 How to Start an Automotive Business With Almost No Capital • 10 This Is Why Your Car’s Headlights Are Dim •

DTC codes / U00xx · Network wiring and bus faults / U0070

U0070Vehicle Communication Bus E (-) Low

U0070 means the vehicle's communication network has detected a low voltage condition on the negative side of Communication Bus E, which is a dedicated data bus used by certain control modules. The computer that monitors this bus has seen the bus-minus wire pulled below its normal idle voltage, indicating a short to ground or a failed transceiver on one of the modules attached to that bus.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaNetwork wiring and bus faults

Symptoms you may notice

  • The warning light (malfunction indicator lamp) illuminates, often with no other noticeable symptoms.
  • One or more control modules may stop communicating, causing unrelated systems to set their own codes.
  • Intermittent operation of features controlled by modules on Bus E, such as lighting or body functions.
  • The scan tool may fail to communicate with certain modules or show them as 'no response'.
  • A no-start condition if the affected bus is part of the powertrain network.
  • Multiple warning lights on the dashboard if several modules share the bus.

Common causes, most likely first

  1. A short to ground on the Bus E minus wire, often from chafed insulation or a pinched harness.
  2. A failed control module on Bus E that is dragging the bus-minus line low internally.
  3. Corroded or loose connector terminals at a module or inline harness connector on the Bus E circuit.
  4. Water intrusion into a connector or module causing a conductive path to ground.
  5. Aftermarket accessories improperly tapped into the bus wiring, creating a partial short.
  6. A faulty transceiver inside one of the modules on the bus, even if the module otherwise appears to work.

How to diagnose and fix it

  1. Connect a scan tool and record all stored codes, then check which modules are communicating and which are not.
  2. Obtain the vehicle-specific wiring diagram for Bus E and identify all modules and connectors on that bus.
  3. Visually inspect the Bus E minus wire and its connectors for damage, corrosion, or signs of water intrusion.
  4. Disconnect modules one at a time from the bus and recheck bus voltage to see if the low condition clears.
  5. Measure resistance from the Bus E minus wire to chassis ground with all modules disconnected to check for a short.
  6. Repair any chafed wire, replace corroded terminals, or replace the module that is pulling the bus low.
  7. Clear codes and verify communication on Bus E with a scan tool before returning the vehicle.

Bus E faults that fool good technicians

  • A module that sets U0070 is often not the faulty module; the code is stored by any module that sees the bus-minus line low, so the culprit is usually elsewhere on the bus.
  • Aftermarket alarms, remote starters, or phone chargers spliced into bus wiring are a frequent cause of a low bus-minus condition that only appears when the accessory is powered.
  • The bus-minus wire can read normal voltage with a voltmeter while still being intermittently shorted, so a wiggle test and a lab scope are more reliable than a static voltage check.
  • A failed module may still communicate on other buses and appear healthy on a scan tool, yet its internal transceiver can drag Bus E minus low and take down the whole bus.
  • Water intrusion into a connector behind a kick panel or under a seat is a common hidden cause that only shows up after rain or a car wash.

Can I keep driving with U0070?

If the vehicle starts, runs, and drives normally, you can drive it to a repair shop, but avoid long trips and expect that some electrical features may not work. If the engine cranks but does not start or multiple warning lights are on, have the vehicle towed because the bus fault may disable safety or powertrain systems.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage