U0421 — Invalid Data Received From Ride Level Control Module

U0421 — Invalid Data Received From Ride Level Control Module. A fault in the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Typical causes: corroded connectors, especially in wet areas, aftermarket equipment interfering with the bus, a faulty module pulling the bus down.

vehicle network

Is it safe to drive?

Drive with caution Depends on what is affected. A single dead convenience module is fine to drive with; loss of communication with engine, braking or steering modules is not. If multiple critical systems drop out, do not drive.

How to diagnose with an OBD scanner

  1. Read the code and freeze frame Connect an OBD2 scanner, confirm U0421 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
  2. Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many U0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
  3. Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the vehicle network (CAN bus) communication for damage, corrosion, chafing or poor contact.
  4. Subsystem check Measure resistance between CAN-High and CAN-Low at the OBD port with power off — about 60 Ω is healthy.
  5. Subsystem check Scan all modules: the one that does not respond is either the culprit or downstream of the break.
  6. Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm U0421 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for U0421 (parts and labor, USD, independent shop rates): Repair CAN wiring or connectors: $100–$400; Remove interfering aftermarket device: $0–$150; Replace the faulty control module: $300–$1,500. Overall, fixing U0421 usually costs between $0 and $1,500. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

What does OBD2 code U0421 mean?

U0421 — Invalid Data Received From Ride Level Control Module. A fault in the vehicle network (CAN bus) communication. Short, gentle driving to a shop is usually possible. Typical causes: corroded connectors, especially in wet areas, aftermarket equipment interfering with the bus, a faulty module pulling the bus down.

How do I diagnose U0421 myself?

Start with a scan: confirm U0421, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the vehicle network (CAN bus) communication, and verify the suspect component against live data before buying parts.

What is the most common cause of U0421?

The most common causes are: corroded connectors, especially in wet areas, aftermarket equipment interfering with the bus, a faulty module pulling the bus down.

How much does it cost to fix U0421?

Repair CAN wiring or connectors — $100–$400; Remove interfering aftermarket device — $0–$150; Replace the faulty control module — $300–$1,500. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

What are the symptoms of U0421?

Drivers most often notice: no-start or intermittent starting in some cases, multiple warning lights on at once, intermittent loss of functions (gauges, windows, steering assist), random, hard-to-reproduce electrical glitches.

What does U0421 mean?

When U0421 appears on a scan, it means the control module has flagged a problem in the vehicle network (CAN bus) communication: invalid data received from ride level control module. The fault sits in the vehicle network group of the OBD2 standard.

The module monitors this system continuously while driving. When readings fall outside the expected range for a defined number of drive cycles, it stores U0421 and switches on the warning light. Freeze frame data saved with the code shows the exact conditions — rpm, load, temperature, speed — at the moment the fault was detected, which is the best starting point for diagnosis.

What causes U0421?

  • water ingress in harness junctions
  • poor grounds or low battery voltage
  • a faulty module pulling the bus down
  • damaged CAN bus wiring or short to power/ground

Common symptoms of U0421

  • no-start or intermittent starting in some cases
  • multiple warning lights on at once
  • intermittent loss of functions (gauges, windows, steering assist)
  • random, hard-to-reproduce electrical glitches
  • modules intermittently not communicating with the scanner

How to diagnose U0421

  1. Connect an OBD2 scanner, confirm U0421 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
  2. Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many U0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
  3. Visually inspect the wiring harness and connectors related to the vehicle network (CAN bus) communication for damage, corrosion, chafing or poor contact.
  4. Measure resistance between CAN-High and CAN-Low at the OBD port with power off — about 60 Ω is healthy.
  5. Scan all modules: the one that does not respond is either the culprit or downstream of the break.
  6. Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm U0421 does not return.

How to fix U0421

Start with the cheapest and most common causes before replacing expensive parts:

  • Repair CAN wiring or connectors — $100–$400
  • Remove interfering aftermarket device — $0–$150
  • Replace the faulty control module — $300–$1,500

How much does it cost to fix U0421?

Repair cost depends on which component actually failed. Typical scenarios for U0421 (parts and labor, USD, independent shop rates):

  • Repair CAN wiring or connectors: $100–$400
  • Remove interfering aftermarket device: $0–$150
  • Replace the faulty control module: $300–$1,500

Overall, fixing U0421 usually costs between $0 and $1,500. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Can you drive with U0421?

Depends on what is affected. A single dead convenience module is fine to drive with; loss of communication with engine, braking or steering modules is not. If multiple critical systems drop out, do not drive.

Related OBD2 codes