Find the Root Cause


Taiichi Ohno, the father of the Toyota Production System and the creator of the 5-Why method of root cause analysis, used this example – a robot failure – to teach others the 5-Why technique at Toyota:

1.    Why did the robot stop?

–    The circuit has overloaded, causing a blown fuse.

2.    Why did the circuit overload?

–    There was insufficient lubrication on the bearings, so they locked up.

3.    Why was there insufficient lubrication on the bearings?

–    The oil pump on the robot is not circulating sufficient oil.

4.    Why is the pump not circulating sufficient oil?

–    The pump intake is clogged with metal shavings.

5.    Why is the intake clogged with metal shavings?

–    Because there is no filter on the pump.

For Mr. Ohno, that was the end of the root cause process: Install a filter and get back to work. But this isn’t even the start of the root cause analysis process in TapRooT®.

Let’s look at this incident using TapRooT® and see how 5-Whys compares to the advanced TapRooT® Root Cause Analysis System.

Where to Start

TapRooT® is more than a tool. It is a systematic process with embedded tools to help an investigator find and fix the root causes of a problem. It starts with the TapRooT® 7-Step Process (picture below of the process being taught in a 2-Day TapRooT® Class).

Daver Tatweer Bahrain New Instructor May2011 2

In the process diagram, the left column contains the steps used to investigate and correct the problem and the right column shows the required (bold text) and optional (plain text) TapRooT® Tools.

To start investigating the problem, one draws a SnapCharT® (shown below).

Screen Shot 2013-07-10 At 12.34.46 Pm

Spring SnapCharT®

A Spring SnapCharT® is the start of “growing” a SnapCharT® and helps the investigator understand what happened. In this case we’ve placed everything we know from the previous example on the chart.

Notice that the 5-Whys that Mr. Ohno asked turned out to be mainly the sequence of events leading up to the failure. You might also notice how easy the example is to understand when viewed on a SnapCharT®. One more thing to notice on this simple Spring SnapCharT® is that we’ve already gone beyond the 5-Whys by indicating that there was no low oil pressure alarm.

Next Step – Collect Info

A Spring SnapCharT® is the start of an investigation. Next, the investigator collects info (grows the SnapCharT®) to expand his/her understanding of what happened. A good TapRooT® Investigator would have several areas to look at.

First, what happened to the filter? Was it forgotten during maintenance or was it never designed into the system?

Next, where did the metal shavings come from? Metal shavings in a lube oil system are unusual. What was the source?

The new information provides a fairly complete understanding of what happened and is shown on the SnapCharT® below.

Screen Shot 2013-07-10 At 12.40.32 Pm
(Double click to expand)

Causal Factors

Once one understands what happened, the next step is to understand why it happened. In TapRooT®, this starts by identifying the Causal Factors that, if eliminated, would have stopped the accident from occurring or reduced the seriousness of the incident. The four Causal Factors for the Robot Stops incident are shown on the SnapCharT® on page 2 and are indicated by triangles ().

Where Mr. Ohno only had one root cause, TapRooT® has already identified four causal factors. Each of these Causal Factors could have multiple root causes so TapRooT® is already highlighting one of the weaknesses of 5-Whys – that it usually focuses on a single cause and misses additional causes that also need corrective action.

TapRooT® Root Causes

In Step 4 of the TapRooT® Process, each Causal Factor is analyzed using the Root Cause Tree® to guide the investigator to the Causal Factor’s root causes. The tree is described in detail in the TapRooT® Book (CLICK HERE for info).

08Taprootbook Cover-8

For this example, we won’t show the entire analysis of all four Causal Factors using the Root Cause Tree® and Dictionary. For people who would like to know more about the 15-question Human Performance Troubleshooting Guide and the way the tree is used to help investigators find causes beyond their current knowledge, we recommend reading the “How Does TapRooT® Work” article on the Root Cause Analysis Blog ( or attending a 2-Day or 5-Day TapRooT® Course.

However, we will describe the analysis of the Causal Factor “Operator doesn’t know oil pressure is low.”

This starts out on the tree as a Human Performance Difficulty that leads us to the Human Performance Troubleshooting Guide. When asking the 15 Questions, two questions get a “yes” for this Causal Factor and guide us to the Human Engineering, Procedures, and Training Basic Cause Categories on the back side of the Root Cause Tree®.

Screen Shot 2013-07-10 At 12.51.23 Pm

In analyzing these categories, no causes are found in the Procedures or Training Basic Cause Categories. However, two root causes are found to be applicable in the Human Engineering Basic Cause Category (above).

Thus, it was determined that if the operator had some type of oil pressure display/alarm to make the detection of a problem possible (error would be detectable), then the robot could have been stopped and fixed before damage to the bearings had occurred. Thus, the incident would have been made significantly less severe.

There are still three other Causal Factors to analyze; Generic Causes to analyze; and Corrective Actions to develop. There’s more to be learned! However, just this limited analysis shows that, even when used by an expert like Taiichi Ohno, 5-Whys misses important facts and root causes. Perhaps now you will agree that 5-Whys isn’t adequate for analysis of even a simple problem when compared to advanced root cause analysis using TapRooT®. Learn about TapRooT® at an upcoming course.