U0070 indicates a loss of communication on the vehicle’s high‑speed CAN (Controller Area Network) bus. The powertrain control module is not receiving or transmitting data on the network as expected.
A broken wire, corroded connector, or short to ground can interrupt the high‑speed bus signal.
Incorrect or missing termination at the ends of the bus can cause voltage level errors and trigger a low‑bus condition.
A malfunctioning transceiver inside a module (e.g., PCM, TCM, ABS controller) can stop that node from communicating, pulling the bus low.
Poor contact at any of the network connectors can create intermittent communication loss.
Only after ruling out wiring and external module issues should the PCM be considered, as it is rarely the primary cause.
Replacing the PCM is rarely necessary. In most cases the problem is wiring, connectors, or a peripheral module’s transceiver. PCM replacement should be a last resort after thorough network testing.
A fuse that supplies power to the CAN network can cause a loss of communication, but most vehicles protect the bus with dedicated fuses that, when blown, also trigger other specific codes. Check relevant fuses, but they are not the most common cause.
U0070 is a network‑communication code, not an emissions fault. However, loss of bus communication can prevent emission‑related modules from operating, potentially leading to additional emission codes.
Yes. If the vehicle’s battery voltage drops too low during start‑up, the CAN transceivers may not initialize correctly, resulting in a low‑bus condition. Verify battery health and charging system if the code appears only during cold starts.