Mitsubishi P1B77
Return to Step 1. NO : The diagnosis is complete. DTC P1B78 Quick Charger Received Current CAUTION If there is any problem in the CAN bus lines, an incorrect DTC may be set. Prior
Quick answer
For U.S.-specification 2014 and 2016 Mitsubishi i-MiEV vehicles, P1B77 is documented in Mitsubishi diagnostic material. The supplied evidence shows that, if P1B77 remains stored during the specified diagnostic process, the Battery Management Unit (BMU) is replaced and the code is then rechecked. The exact fault meaning for P1B77 is not established by the supplied verified evidence.
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 P1B77 mean?
For U.S.-specification 2014 and 2016 Mitsubishi i-MiEV vehicles, P1B77 is documented in Mitsubishi diagnostic material. The supplied evidence shows that, if P1B77 remains stored during the specified diagnostic process, the Battery Management Unit (BMU) is replaced and the code is then rechecked. The exact fault meaning for P1B77 is not established by the supplied verified evidence.
2. Technical explanation
Mitsubishi’s published diagnostic sequence instructs technicians to erase P1B77, connect the quick-charging gun/connector or external power-supply equipment, and check whether the DTC returns. One supplied procedure states that, when P1B77 is stored, the BMU is to be replaced before proceeding to the recheck step. If P1B77 returns after that recheck, the procedure directs the technician to return to Step 1. If it does not return, the diagnosis is complete. The source excerpts also caution that CAN-bus faults can cause an incorrect DTC to be stored or set; however, that caution appears in the following P1B78 diagnostic section and does not by itself establish a CAN-bus fault as the cause of P1B77.
3. What system is affected?
The BMU is directly identified by the Mitsubishi diagnostic instruction. The EV-ECU is also identified as the module in which the DTC is checked. A more specific system description is not yet established by verified evidence.
4. How serious is this code?
Not yet established by verified evidence.
5. Symptoms you may notice
Not yet established by verified evidence.
6. Possible causes
- A confirmed root cause for P1B77 is not yet established by verified evidence.
- The supplied Mitsubishi procedure identifies BMU replacement when P1B77 is stored in the specified diagnostic path, but it does not establish that every occurrence is caused by BMU failure.
- The supplied material cautions that CAN-bus problems can result in an incorrect DTC, but the excerpt does not specifically establish CAN-bus faults as a cause of P1B77.
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. The documented recheck procedure uses a quick-charging connector/gun or external power-supply equipment, but this is a technician diagnostic procedure and does not establish that normal charging is safe or unsafe with P1B77 present.
9. What you can safely do
- Have the vehicle evaluated using the applicable Mitsubishi diagnostic procedure.
- Avoid attempting BMU replacement or high-voltage diagnostic work yourself.
- Provide the stored DTC and the vehicle model year to a qualified Mitsubishi EV service provider.
10. Step-by-step troubleshooting
- Verified technician procedure: check whether P1B77 is stored in the EV-ECU.
- If directed by the diagnostic path, erase the stored DTC.
- Connect the quick-charging gun/connector or external power-supply equipment as specified in the Mitsubishi procedure.
- Check whether P1B77 is stored or set again.
- The supplied material indicates that a returning P1B77 requires returning to the beginning of the diagnostic procedure.
11. When to contact service
Service is appropriate because the verified Mitsubishi procedure includes BMU replacement when P1B77 is stored in the applicable diagnostic path. Use a qualified Mitsubishi EV service provider.
12. What the service center may check
- Check for P1B77 in the EV-ECU.
- Follow the Mitsubishi erase-and-recheck procedure using the specified quick-charging or external-power equipment.
- Where P1B77 is stored in the documented diagnostic path, replace the BMU.
- After BMU replacement, erase the DTC, reconnect the specified equipment, and check whether P1B77 returns.
- If P1B77 returns, return to Step 1 of the Mitsubishi diagnostic procedure; if it does not return, the diagnosis is complete.
13. Possible repair or resolution
- The verified Mitsubishi diagnostic instruction specifies BMU replacement when P1B77 is stored in the referenced diagnostic path.
- A successful documented outcome is that P1B77 does not return after the prescribed recheck.
14. Affected vehicles
- Mitsubishi i-MiEV · 2014 · US
- Mitsubishi i-MiEV · 2016 · US
15. Related TSBs / service bulletins
- Mitsubishi TSB-19-54-004, published March 13, 2019, available through NHTSA as Manufacturer Communication PDF 10158409: https://static.nhtsa.gov/odi/tsbs/2019/MC-10158409-9999.pdf
- Mitsubishi TSB-19-54-005, published March 13, 2019, available through NHTSA as Manufacturer Communication PDF 10158410: https://static.nhtsa.gov/odi/tsbs/2019/MC-10158410-9999.pdf
16. Recall information
No recall relationship is established by verified evidence.
17. Official manufacturer information
Verified applicability: Mitsubishi i-MiEV, U.S. market, model years 2014 and 2016. The supplied official NHTSA-hosted Mitsubishi communications are TSB-19-54-004 and TSB-19-54-005. Recall applicability is not established by the supplied verified evidence.
19. Frequently asked questions
What does P1B77 mean on a Mitsubishi i-MiEV?
The exact fault meaning is not established by the supplied verified evidence. The evidence does document a Mitsubishi diagnostic process for P1B77 and identifies BMU replacement within that process.
Does P1B77 require BMU replacement?
In the supplied Mitsubishi diagnostic path, if P1B77 is stored, the instruction is to replace the BMU and then perform the recheck procedure. Applicability outside that documented procedure is not established by verified evidence.
What happens after the BMU is replaced?
The documented procedure erases the DTC, connects the specified quick-charging or external-power equipment, and checks whether P1B77 returns. If it does not return, the diagnosis is complete; if it returns, the procedure directs the technician back to Step 1.
Can a CAN-bus issue cause P1B77?
The supplied material cautions that CAN-bus problems can cause an incorrect DTC, but this caution is presented in the P1B78 section. It does not specifically establish CAN-bus problems as a cause of P1B77.