The OBD2 code U0253 indicates a communication failure between the vehicle’s primary control unit and the Accessory Protocol Interface Module (APIM), which manages various accessory functions like the radio, HVAC controls, and more. Such a failure can lead to multiple systems becoming inoperative, as seen in the described service cases. This issue underscores the complexity and interconnectivity of modern vehicle electronic systems, where a single communication fault can impact multiple functionalities.
U0253 quick overview
| Meaning | U0253: Lost Communication with Accessory Protocol Interface Module |
| Is it serious? | Yes, as it can affect the functionality of several important vehicle systems. |
| Possible causes | – Faulty wiring or connectors in the CAN bus system – Malfunctions within the APIM itself – Issues with the vehicle’s Body Control Module (BCM) – Corrosion or damage to electrical connectors |
| How to diagnose? | Perform pinpoint tests as recommended by vehicle-specific diagnostic charts (AA, AD, AG for Ford) Check CAN bus connections for corrosion, damage, or looseness Test continuity and resistance of CAN bus wiring Inspect connectors for moisture intrusion or damage Monitor CAN voltages at various modules to identify signal issues |
U0253 Meaning
For those not deeply versed in auto mechanics, imagine your vehicle’s electronic system as a network of computers talking to each other. The U0253 code is like saying one computer (the APIM) has stopped receiving messages from the rest of the network, causing features like the radio or air conditioning controls to stop working.
This could be due to a bad connection, like a loose plug in your home network, or a damaged wire acting as the network cable. Fixing this involves checking and repairing these connections to restore the conversation among the vehicle’s electronic systems.
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How to fix U0253 – learn from mechanics
I looked into U0253 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.
Case #1: Ford
Vehicle Information 2011 Ford Fusion SEL 3.0L
Issue + Repair History
- Codes U0253, U0140, U0155 detected.
- Radio, HVAC controls, Shift interlock, door locks all inoperative.
- Checked all power and grounds fuses.
- Ohm tested bus wiring for body control module and related modules.
- Loose pin found in connector on the smart junction box.
Other OBD2 Codes + Test Results
- U0253: Pinpoint test AA recommended.
- U0140: Pinpoint test AD recommended.
- U0155: Pinpoint test AG recommended.
- Communication codes detected; follow pinpoint charts to identify common factors.
Mechanic Suggestions
- Use scope and wiring diagrams to analyze bus signals.
- Disconnect devices one at a time to identify culprit.
- Check for missing modules in role call list during module scan.
- Monitor CAN voltages at various modules.
- Check electrical schematics for common powers/grounds between systems.
- Disconnect battery cables, short them together for 10 minutes, and reevaluate.
- Clear all DTCs and recheck operation.
- Investigate recent module replacements or programming.
- Inspect OCSM for potential CAN line damage due to junk under passenger seat.
- Verify integrity of key removal inhibit fuse in BCM.
Final Fix
- Found loose pin in connector on the smart junction box; depinned and crimped it, restoring functionality to all affected systems.
Case #2: Chevrolet
Vehicle Information 2008 Chevrolet Silverado 1500 LTZ 5.3L
Issue + Repair History
- Code U0253 detected.
- Radio, HVAC controls, and instrument cluster intermittently malfunctioning.
- Checked all power and ground connections.
- Inspected wiring harness for signs of damage or wear.
Other OBD2 Codes + Test Results
- U0253: Communication error between modules.
- No other codes detected.
- Live data showed intermittent signal loss between various modules.
Mechanic Suggestions
- Perform pinpoint test for U0253 code.
- Check CAN bus connections for signs of corrosion or damage.
- Test continuity and resistance of CAN bus wiring.
- Inspect connectors for signs of moisture intrusion.
- Check for loose or damaged pins in connectors.
Final Fix
- Found corroded connector causing intermittent signal loss between modules. Cleaned and repaired connector, resolving communication error and restoring functionality to affected systems.
Case #3: Toyota
Vehicle Information 2015 Toyota Camry LE 2.5L
Issue + Repair History
- Code U0253 detected.
- HVAC controls and power windows intermittently malfunctioning.
- Checked all fuses related to affected systems.
- Inspected wiring harness for signs of damage or wear.
Other OBD2 Codes + Test Results
- U0253: Communication error between modules.
- No other codes detected.
- Live data showed intermittent signal loss between body control module and affected systems.
Mechanic Suggestions
- Perform pinpoint test for U0253 code.
- Check for loose or damaged connectors at body control module.
- Test continuity and resistance of CAN bus wiring.
- Inspect connectors for signs of corrosion or damage.
- Check for aftermarket electrical modifications.
Final Fix
- Found loose connector at body control module causing intermittent signal loss. Secured connector and cleared code, restoring communication between modules and functionality to affected systems.
How to diagnose U0253
I made you an overview of solving this DTC, based on all the advice that was suggested by certified mechanics to address this issue in previously mentioned service cases.
| Diagnostic Step | Explanation |
|---|---|
| Perform pinpoint tests | Follow vehicle-specific charts to methodically diagnose the issue. |
| Check CAN bus connections | Look for signs of corrosion, damage, or looseness in the network. |
| Test continuity and resistance | Ensure the wiring has no breaks and proper resistance levels. |
| Inspect connectors | Check for moisture, corrosion, or physical damage causing issues. |
| Monitor CAN voltages | Identify if there are fluctuations or drops in network signals. |
Addressing a U0253 code typically involves a meticulous process of checking and repairing the vehicle’s network system to ensure all modules communicate correctly. Given the potential complexity of these issues, professional diagnostic equipment and expertise may be required to effectively restore system functionality.
Car Diagnostics Training
- Car Electrical basics
- OBD-II scanner basics
- How to use an OBD reader
- Introduction to a Bi-directional Scan tool
- OBD scanner buyer’s guide + discounts
I test OBD-II scanners and make DIY Engine diagnostics guides to help you solve your car problems without having to depend on the mechanic. A lot of them will try to scam you or are just no help at all. About Juraj Lukacko