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U0408 — Invalid Data Received From Throttle Actuator Control Module

Generic OBD-II · all makesNetwork / communication

U0408 indicates that the Powertrain Control Module (PCM) received data from the Throttle Actuator Control Module (TACM) that it cannot interpret as valid. This usually points to a communication or data integrity problem between the PCM and the electronic throttle body/module rather than a mechanical throttle fault.

Symptoms

What causes it — most likely first

1. Faulty Throttle Actuator Control Module (TACM)

The TACM itself may be sending corrupted or out‑of‑range data due to internal electronics failure, which is the most common cause of U0408.

2. Wiring or connector issues between PCM and TACM

Damaged, corroded, or loose pins/harness can interrupt or distort the CAN message, causing the PCM to flag the data as invalid.

3. CAN bus communication fault

High resistance, short to ground/power, or a malfunctioning node on the CAN network can prevent proper message exchange between modules.

4. PCM software glitch or outdated calibration

A software error in the PCM may misinterpret otherwise valid TACM data; a reflash or update can resolve the issue.

5. PCM hardware failure (rare)

Internal PCM damage that affects its CAN transceiver is possible but uncommon; it should be considered only after other causes are ruled out.

How it's diagnosed

  1. Scan for additional codes and review freeze‑frame data to understand conditions when U0408 set.
  2. Visually inspect the wiring harness and connectors linking the PCM to the TACM for signs of wear, corrosion, or loose connections.
  3. Test continuity and resistance of the CAN‑H and CAN‑L lines between the two modules; repair any opens, shorts, or excessive resistance.
  4. Monitor live data: compare actual throttle position sensor voltage with the commanded throttle value; look for erratic or missing updates.
  5. Perform a module communication test (e.g., ping the TACM with a scan tool) to verify the TACM is responding on the bus.
  6. If wiring and TACM communication are OK, attempt a PCM software update/reflash; if the code persists, evaluate the PCM hardware.

Code facts & related codes

SystemNetwork / communication
StandardizationSAE generic — identical on every make
Related codesU0400 — Invalid Data ReceivedU0401 — Invalid Data Received From EcmpcmU0402 — Invalid Data Received From TcmU0403 — Invalid Data Received From Transfer CaU0404 — Invalid Data Received From Gear Shift U0405 — Invalid Data Received From Cruise Cont

Frequently asked

Is replacing the PCM usually the correct fix for U0408?

No. The PCM is rarely at fault for this code; most cases are due to the throttle actuator module, its wiring, or CAN bus issues. Replacing the PCM without first checking those components often does not resolve the problem.

Can clearing the code make the problem go away permanently?

Clearing the code only turns off the Check Engine Light; if the underlying communication or module fault remains, the code will return once the condition is detected again.

Should I check the battery or charging system when diagnosing U0408?

Yes. Low system voltage can cause intermittent CAN communication errors, so verifying proper battery charge and alternator output is a prudent early step.