Why Won't My Chrysler Town & Country Downshift Normally? It May Not Be the Transmission

When a vehicle isn't shifting or downshifting correctly, it's natural to suspect the transmission.

But modern vehicles don't operate as a collection of independent systems. The engine, transmission and powertrain control systems communicate with each other, and a problem on the engine side can change the way the entire vehicle operates.

A recent 2011 Chrysler Town & Country with more than 268,000 miles was a good example.

The Customer's Concern

Before bringing the vehicle to MDC Automotive Repair, the customer told Mike that the Town & Country was not downshifting correctly.

Mike told him to bring it in so we could scan the vehicle and see what the computer was detecting before deciding where the problem was coming from.

When the vehicle arrived, diagnostic testing revealed trouble code P06DD, related to engine oil-pressure regulation.

Now we had somewhere to begin.

What Does Engine Oil Pressure Have to Do With a Shifting Complaint?

The 3.6L engine in this Town & Country uses a variable-displacement, two-stage oil pump. The system is designed to operate at different pressure levels depending on engine operating conditions.

When the engine requires the higher-pressure stage, the oil-pump system must respond accordingly.

If the PCM commands that change and doesn't see the expected oil-pressure response, it can set P06DD and place the vehicle into a reduced-performance operating strategy.

That reduced-performance condition can affect normal powertrain operation, including how the transmission responds and downshifts.

So before condemning the transmission, we needed to determine whether the oil-pressure fault was real.

A Trouble Code Is Not a Diagnosis

We first verified that the engine had the proper oil level and that the correct Mopar oil filter was installed.

Both checked out.

The scan-tool information indicated that engine oil pressure wasn't responding as expected under higher engine speed and load.

But we didn't stop there.

We installed a mechanical oil-pressure gauge on the engine.

Why?

Because if we're going to recommend a significant engine repair, we want to know whether the pressure reported electronically agrees with what the engine is actually producing.

The mechanical gauge confirmed the scan-tool data.

Actual engine oil pressure remained lower than expected when the system should have transitioned into higher-pressure operation.

What We Found

Our testing indicated that the variable-displacement oil pump was not properly transitioning into its high-pressure stage.

That explained the P06DD fault and the reduced-performance condition affecting the way the vehicle operated.

At 268,047 miles, we recommended replacement of the engine oil-pump assembly.

The customer elected not to perform the repair at that time.

And that's where this particular diagnostic case ends.

We won't tell you that replacing the pump fixed the vehicle, because the repair wasn't performed at MDC.

Diagnosis and repair verification are two different things.

The Lesson: Don't Diagnose a Transmission From the Driver's Seat

A vehicle that doesn't shift normally doesn't automatically need transmission work.

Engine-management problems, electrical faults, communication problems, reduced-power strategies and other conditions can all affect the way a modern powertrain operates.

That's why we start with the complaint and follow the evidence.

In this case:

The customer noticed a downshift problem.
The scan revealed P06DD.
Testing led us to the engine oil-pressure system.
A mechanical gauge independently confirmed the low-pressure condition.
The two-stage oil pump wasn't responding properly.

We didn't start replacing transmission parts because the symptom felt like a transmission problem.

We diagnosed the system.

MDC Automotive Repair

At MDC Automotive Repair, we believe a trouble code is a starting point—not a parts list.

Whether you're dealing with a transmission concern, Check Engine Light, electrical problem, drivability issue or an intermittent fault, our goal is to determine why the vehicle is behaving the way it is before recommending repairs.

We Don't Guess. We Diagnose.