What to do with high voltage problems with hybrids

If a vehicle with a check engine light rolls into your bay, what is your diagnostic routine?

First you may scan the code, check technical service bulletings (TSBs) and do a visual inspection of the vehicle and then follow the test plan offered by your scan tool or information system to diagnose the vehicle.

Throughout the whole process, your particular experience with the problem, and with vehicles in general, informs you when to conduct certain tests with particular tools and when to disregard the test plan if necessary.

Does any of this change when we have a different light on, like an airbag or ABS light? Of course not! So, don’t get intimidated if you ever come across a Honda hybrid vehicle that has an Integrated Motor Assist (IMA) light on. Your instincts won’t fail you.

Code 78: Battery Module Deterioration

So, a 2005 Honda Civic Hybrid rolls into your door. It has over 150,000 miles on it and that means Honda no longer has any liability if the HV battery dies. Now the customer brings it to you because the IMA light is on.

The customer informs the shop that the dealer replaced the battery at 147,000 miles (see Fig. 1), so he does not know why the light is on. Is the battery defective? Did they really even replace it?

The first step is to read the DTC, and what is found is a Code 78. In Mitchell 1’s ProDemand, searching for this code gives us a test plan for a P0A7F (see Fig. 2). Here ProDemand asks us to delete the DTC, then hold the engine speed at 3,500 to 4,000 rpm until the HV battery’s state of charge reaches 70 percent.

After running the test, you check for pending DTCs and what do you see? No new codes. Looking at the PIDs, the HV battery is at 159V, which is good for a Honda (see Fig. 3).

But, what’s the test plan tell you to do? Replace the HV battery. Using the factory scan tool, the HDS, it informs you that the only possible cause for the error is “battery module failure” (see Fig. 4).

Go beyond the test plan

Wait, this doesn’t make sense! The customer informed you that the battery was replaced and the vehicle has prominent “PC1” stickers that indicate the vehicle now has a second generation battery (see Fig. 5)

What do you do now? Read TSBs. After all, if the problem is relatively common, the OEM is going to alert you of it.

On ProDemand, the first TSB you will find is A12010 which states simply “to fix this problem, replace the IMA battery” (see Fig. 6, on next page). However, if we read carefully, ProDemand adds “Don’t forget to match the IMA software to the IMA battery” and links to a subsequent TSB for “IMA battery software and hardware updates” (see Fig. 7, on next page).

This TSB, number 10-083, informs us that the IMA system will have premature battery life with the old software, lists the different generations of HV batteries (PC1 is a second, upgraded model) and informs you that this battery needs software with a 2, 3 or 4 and has the digit after the letter “A” in the Calibration ID.

When we look at the Calibration ID on the vehicle, we realize it ends in “L040,” not A2XX, A3XX or A4XX. This vehicle needs a reflash!

Using the factory scan tool, which is the OTC MVCI, and a $10 software subscription available directly from Honda, anyone can do this. Simply update the tool, click on “CM Update” and the tool will automatically walk you through the process.

Standard diagnostic routine works

Replacing the software, not the battery, will fix this vehicle. So, by following a standard diagnostic routine, where we made use of an information system, TSBs and shop equipment such as scan tools, this vehicle can be diagnosed and repaired without costing the customer an unnecessarily expensive HV battery.