Mitsubishi P1AA9
Cell number mismatch . TROUBLE JUDGMENT Check Conditions When the CMUs are numbered for identification. The following diagnostic trouble codes is stored at the same time. a. U1
Quick answer
P1AA9 is a Mitsubishi i-MiEV battery-management diagnostic trouble code for a cell-number mismatch. Verified service information states that it is set when CMUs are numbered for identification, U1925 (CMU ID numbering reception error) is also stored, and the number of cells is judged invalid.
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 P1AA9 mean?
P1AA9 is a Mitsubishi i-MiEV battery-management diagnostic trouble code for a cell-number mismatch. Verified service information states that it is set when CMUs are numbered for identification, U1925 (CMU ID numbering reception error) is also stored, and the number of cells is judged invalid.
2. Technical explanation
The verified Mitsubishi diagnostic material identifies P1AA9 as “Cell Number Mismatch.” Its stated judgment criterion is that the number of cells is invalid. The listed check condition includes CMUs being numbered for identification and concurrent storage of U1925, “CMU ID numbering reception error.” The provided evidence does not establish a complete vehicle-owner symptom description.
3. What system is affected?
The evidence concerns the main drive lithium-ion battery monitoring system, including the CMUs (cell monitoring units) and BMU (battery management unit).
4. How serious is this code?
Not yet established by verified evidence.
5. Symptoms you may notice
- A stored P1AA9 diagnostic trouble code.
- U1925 may be stored at the same time, according to the verified diagnostic procedure.
6. Possible causes
- The verified material identifies an invalid cell count as the judgment criterion.
- The source excerpt begins a probable-cause entry with “Improper,” but the supplied verified evidence does not contain the complete cause statement. Therefore, a specific cause is 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
- Arrange diagnosis by a Mitsubishi-qualified EV service facility.
- Do not attempt high-voltage battery, CMU, BMU, or battery-wiring repairs yourself.
10. Step-by-step troubleshooting
- Mitsubishi service information directs use of scan tool MB991958 to check whether the diagnostic trouble code remains stored.
- The procedure includes checking data-list information for CMUs 01 through 12, including Item No. 58, CAN controller.
- If the applicable CMU CAN-controller check result is not normal, the cited procedure directs replacement of the Main Drive Lithium-ion Battery, followed by the next diagnostic step.
- If P1AA9 remains stored at the cited diagnostic step, the procedure directs replacement of the BMU. If it is not stored, the check is complete.
- Another cited procedure states that, if the code is set after its checks, replace the BMU; if not, treat it as an intermittent malfunction using Mitsubishi’s intermittent-malfunction procedure.
11. When to contact service
Service is appropriate. The verified procedure involves manufacturer scan-tool diagnostics and may call for Main Drive Lithium-ion Battery or BMU replacement.
12. What the service center may check
- Confirm whether U1925, CMU ID numbering reception error, is stored with P1AA9.
- Check CMU data-list entries for CMUs 01 to 12, including Item No. 58, CAN controller.
- Use scan tool MB991958 to confirm whether P1AA9 remains stored after the applicable checks.
- Follow the Mitsubishi procedure for intermittent malfunctions when the code does not remain set.
13. Possible repair or resolution
- The cited Mitsubishi procedure directs Main Drive Lithium-ion Battery replacement when the applicable CMU CAN-controller check result is not normal.
- The cited procedure directs BMU replacement when P1AA9 remains stored at the specified diagnostic step.
- No further repair resolution is established by the supplied verified evidence.
14. Affected vehicles
- Mitsubishi i-MiEV · 2012 · US
- Mitsubishi i-MiEV · 2014 · US
- Mitsubishi i-MiEV · 2016 · US
15. Related TSBs / service bulletins
- NHTSA manufacturer communication MC-10158409-9999, Mitsubishi TSB-19-54-004, published March 13, 2019: https://static.nhtsa.gov/odi/tsbs/2019/MC-10158409-9999.pdf
- NHTSA manufacturer communication MC-10158410-9999, Mitsubishi TSB-19-54-005, published March 13, 2019: https://static.nhtsa.gov/odi/tsbs/2019/MC-10158410-9999.pdf
- NHTSA manufacturer communication MC-10158408-9999, Mitsubishi TSB-19-54-003, published March 13, 2019: https://static.nhtsa.gov/odi/tsbs/2019/MC-10158408-9999.pdf
16. Recall information
- Not yet established by verified evidence.
17. Official manufacturer information
Verified applicability is Mitsubishi i-MiEV vehicles in the US for model years 2012, 2014, and 2016. The supplied official NHTSA-hosted Mitsubishi communications were published March 13, 2019.
19. Frequently asked questions
What does P1AA9 mean on a Mitsubishi i-MiEV?
It means Cell Number Mismatch. The verified judgment criterion is that the number of cells is invalid.
Which code is associated with P1AA9?
The verified diagnostic material states that U1925, CMU ID numbering reception error, is stored at the same time.
Does P1AA9 have a fail-safe or backup function?
The verified source states: “Not available.”
Can I continue driving or charging?
Not yet established by verified evidence.
What may Mitsubishi service replace?
Depending on the specified diagnostic results, the cited procedure directs replacement of the Main Drive Lithium-ion Battery or the BMU.