Troubleshooting: A Surging Kia

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A 2013 Kia Optima Hybrid. PHOTO KIA Motors

Sustained forward motion proved a problem on this Optima Hybrid.

It seems like everybody is wondering when the opportune time is to get into Hybrid and EV servicing these days. We are getting more calls for diagnosis on Hybrid vehicles. While they are still a very small portion of the overall vehicle fleet, there are a growing number of them on the road. We have developed a 3-day training program that was launched at the end of March 2022 and is a combination of Hands-on and classroom at our training centre in Barrie.

Our latest Hybrid adventure was a 2013 Kia Optima. The car was brought to us with a surge complaint. I test drove the vehicle to observe how the system performed. It didn’t take long for the problem to appear. When I tried to accelerate, the vehicle drove normally up to about 20 km/h at which point the gas engine revved to about 6000 RPM, but the car did not accelerate. 

No codes

I returned to the shop and performed a quick code scan thinking that a problem this significant should be setting codes, there were no codes stored in any modules. 

To understand the nature of the problem we need to look at how this system operates. The Kia system uses two motor generators (MG) and an internal combustion engine (ICE)–see below. MG1 is connected via a heavy serpentine belt to the crankshaft and acts as both a generator and starter. MG2 is sandwiched between the transmission and the ICE and drives the transmission directly. The ICE drives the transmission through a clutch that can connect and disconnect the ICE from the driveline. 

The hybrid system on this Kia used two electric motors, one that acts as generator/starter, the other, located between the gas engine and the transmission that drives the trans directly. PHOTO Mark Lemay

Back to the test drive. When the car starts from a stop, MG2 is powering the car, at about 20 km/h the ICE is started, and its torque is added to the torque from MG2 via the clutch. There is an EV indicator light on the dash to indicate when the powertrain is in pure EV mode or blended power mode. The surge happens at the exact time the EV light goes out and ICE torque is being added to the driveline. It appears as if the clutch is not working properly. 

More complex

When we first looked at the clutch it seemed probable that the clutch was a simple one-way clutch. However, upon investigation, it turned out to be a wet plate clutch driven by an electric pump. This turned out to be good news as it is electronically controlled and there is data on the clutch in the transmission data stream. 

When we observed the clutch data, we found that the TCM was commanding 75 psi and the system was producing about 75 psi. This would indicate that hydraulically, the system was working properly and would indicate that the problem was mechanical related. The car was sent over to BAM Automotive in Barrie, Ont., to have the transmission removed. Upon removal of the transmission and removal of the clutch, we found that the clutch plates were ruined. There was no friction material left on the clutch plates. It turns out that Kia makes a repair kit for this clutch which was installed returning the vehicle to normal operation. As a growing number of these vehicles enter aftermarket service bays, this is a problem we expect to see more of in the future.

Mark Lemay is President of Auto Aide Technical Services. You can reach him at: [email protected].



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