Chevrolet U18B4 SYM00
• DPID 11 Byte1: • DPID 11 Byte2: • DPID 11 Byte3: • DPID 11 Byte4: • DPID 11 Byte5: • DPID 11 Byte6: • DPID 17 Byte0: • DP
Common search variants: U18B4SYM00 · U18B4-SYM00 · U18B4_SYM00 · Search ignores case and common separators.
Quick answer
U18B4 SYM00 is documented in a GM/NHTSA technician communication as a sub-code that must be recorded during diagnosis of an OnStar concern. The verified evidence does not establish a specific fault definition for this code.
This page separates verified manufacturer/regulator evidence from supporting material. Unsupported causes, repairs or safety conclusions are not guessed.
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1. What does U18B4 SYM00 mean?
U18B4 SYM00 is documented in a GM/NHTSA technician communication as a sub-code that must be recorded during diagnosis of an OnStar concern. The verified evidence does not establish a specific fault definition for this code.
2. Technical explanation
For a 2020 Chevrolet Bolt EV in the US, GM’s technician communication instructs technicians to record the sub-code, including U18B4 SYM00 or SYM71, when gathering information for GM Technical Assistance Center (TAC) diagnosis. The communication also directs technicians to retrieve Vehicle Communications Interface Module (VCIM) DTC data, including DPID 11 bytes 0–6 and DPID 17 byte 0. The supplied evidence does not identify what U18B4 SYM00 specifically means, nor does it provide a repair procedure.
3. What system is affected?
OnStar / Vehicle Communications Interface Module (VCIM) diagnostic process is indicated by the verified technician communication. A specific failed system or component is not yet established by verified evidence.
4. How serious is this code?
Unknown. The supplied evidence does not assign a severity level.
5. Symptoms you may notice
- The source discusses diagnosis involving OnStar account status, OnStar key-press behavior, system connection, and GPS location availability on a key press.
- No symptom is confirmed as being caused by U18B4 SYM00.
6. Possible causes
- Not yet established by verified evidence.
7. Can I still drive the vehicle?
Not yet established by verified evidence.
8. Can I charge the vehicle?
Not yet established by verified evidence.
9. What you can safely do
- Record the complete DTC sub-code exactly as displayed, including SYM00.
- If service is pursued, provide the technician with the code and any observed OnStar connection or location behavior.
- Do not infer vehicle-driving, charging, or high-voltage-system status from this code based on the supplied evidence.
10. Step-by-step troubleshooting
- GM’s communication says technicians may ask whether the customer has an active OnStar account with data available, as applicable.
- Technicians may check what occurs when an OnStar key press is made, whether the system connects, and whether OnStar has a current GPS location after a key press.
- The communication instructs technicians to record VCIM data through: Module Diagnostics / Vehicle Communications Interface Module / Data Display / DTC Data.
- The listed data includes DPID 11 Byte0 through Byte6 and DPID 17 Byte0.
- Further diagnostic interpretation is not yet established by verified evidence.
11. When to contact service
Contact a Chevrolet dealer or qualified GM service provider if the code is active or an OnStar-related concern is present. The verified communication refers to GM TAC diagnostic information gathering.
12. What the service center may check
- Record the exact sub-code: U18B4 SYM00.
- Check active OnStar account/data status as applicable.
- Check response to an OnStar key press.
- Check whether the system connects after the key press.
- Check whether OnStar has a current GPS location after the key press.
- Retrieve and record VCIM DTC data, including DPID 11 bytes 0–6 and DPID 17 byte 0.
13. Possible repair or resolution
- Not yet established by verified evidence.
14. Affected vehicles
- Chevrolet Bolt EV · 2020 · US
15. Related TSBs / service bulletins
- NHTSA Manufacturer Communication PDF 10172292: 030846004W, published January 13, 2020. It references U18B4 SYM00 or SYM71 as sub-codes to record during GM TAC diagnostic information collection for OnStar-related concerns. It does not provide a confirmed fault meaning or repair for U18B4 SYM00 in the supplied evidence.
16. Recall information
- Not yet established by verified evidence.
17. Official manufacturer information
Verified source: NHTSA Manufacturer Communication PDF 10172292: 030846004W (GM), published 2020-01-13. https://static.nhtsa.gov/odi/tsbs/2020/MC-10172292-9999.pdf
19. Frequently asked questions
What does U18B4 SYM00 mean on a 2020 Chevrolet Bolt EV?
The supplied verified evidence does not provide a specific definition. It identifies U18B4 SYM00 as a sub-code that GM technicians should record during an OnStar-related diagnostic process.
Is U18B4 SYM00 related to the high-voltage battery or charging system?
Not yet established by verified evidence.
Can I drive or charge with U18B4 SYM00?
Not yet established by verified evidence.
What information should be collected for service?
The GM communication calls for the full sub-code, OnStar account/data status as applicable, OnStar key-press results, connection status, GPS-location availability, and VCIM DTC data including DPID 11 bytes 0–6 and DPID 17 byte 0.