Report on fuel economy and emission testing confirms no improper alteration or falsification of test data by Mazda

Following a request made by Japan’s Ministry of Land, Infrastructure, Transport and Tourism (MLIT), issued to Japanese automakers on July 9 2018 after the discovery of fraudulent testing practices at other companies, Mazda Motor Corporation submitted a report to MLIT on the results of an investigation into its sample testing of fuel economy and emissions during final vehicle inspections.


The investigation covered JC081 and WLTC2 testing modes and the key findings of the report are:


  1. No improper alteration or falsification of test data in either mode.


  1. Test data containing speed trace errors* was found in 72 cases out of 1,472 vehicles tested under the JC08 mode. The company has identified two reasons for these errors. Firstly, the system was not set up to automatically invalidate results when a speed trace error occurred. Secondly, test procedures left the determination of speed trace errors up to each individual inspector.


  1. All test data has been re-examined and the results show there was no effect on specification fuel economy and emission figures. No such cases were found in WLTC mode testing.


Mazda has decided to take the following steps to prevent a reoccurrence:


  • The system will be updated to automatically treat test results as invalid in the event of a speed trace error.


  • Mazda has increased the number of employees who check inspection data, including speed trace errors.


Mazda accepts that errors were made on a small number of tests and the situation was identified quickly and steps have been put in place to avoid it happening in the future.


* A situation in which vehicle speed deviates more than the permitted amount from the speed trace pattern prescribed by the test mode



1 JCO8: Japanese 2005 emission regulation introduced a new JC08 chassis dynamometer test cycle for light vehicles (< 3500 kg GVW). The test represents driving in congested city traffic, including idling periods and frequently alternating acceleration and deceleration. Measurement is made twice, with a cold start and with a warm start. The test is used for emission measurement and fuel economy determination, for gasoline and diesel vehicles.

2 WLTC: The Worldwide harmonized Light vehicles Test Cycles (WLTC) are chassis dynamometer tests for the determination of emissions and fuel consumption from light-duty vehicles. The tests have been developed by the UN ECE GRPE (Working Party on Pollution and Energy) group. The WLTC cycles are part of the Worldwide harmonized Light vehicles Test Procedures (WLTP), published as UNECE Global technical regulation No 15 (GTR 15). While the acronyms WLTP and WLTC are sometimes used interchangeably, the WLTP procedures define a number of other procedures—in addition to the WLTC test cycles—that are needed to type approve a vehicle

Report to MLIT on the measurement of fuel economy and emissions in final inspections


Outline of investigation into Mazda’s sample testing of fuel economy and emissions during final vehicle inspections


Plant investigated:                        Hiroshima Plant (Minami-ku, Hiroshima)

Note: sample testing of fuel economy and emissions for all domestically produced models takes place at Hiroshima Plant


Period covered:                              For data used in test reports, the investigation covered the full three years and nine months (November 2014 – July 2018) that the company is required by law to keep records. For data for which there is no obligation to keep records, the period covered was decided by available data saved in testing systems, etc.

[1] JC08 fuel economy and emissions data:                    From Jan 2018

[2] JC08 speed trace data:                                                                                     From Oct 2016

[3] WLTC fuel economy and emissions data:    From Jan 2018

[4] WLTC speed trace data:                                                                                     From Jan 2018


Method of investigation:

  1. Data saved in exhaust testing equipment ([2] above) was checked against data in test reports to confirm whether or not any vehicles had made speed trace errors or whether any data had been improperly altered.
  2. Data not saved in exhaust testing equipment but which was printed out from such equipment or was similarly judged to be in an unalterable form was checked against test report data to confirm whether or not there had been any instances of data alteration ([1], [3] and [4] above).
  3. A hearing was conducted with inspectors regarding the existence of altered data.


Items investigated and results

Items investigated Result No. of vehicles


No. of vehicles



of total

Improper alteration of reported fuel economy and emissions data Not found 466 units

JC08: 39 units [1]

WLTC: 427 units [3]

0 units 0.0%
Improper alteration of temperature/ humidity data in the emissions testing room Not found 466 units

JC08: 39 units

WLTC: 427units

0 units 0.0%
Data judged valid despite deviations from stipulated test conditions
  Speed trace


Found 1,875units

JC08: 1,472 units [2]

WLTC: 403 units [4]

72 units

JC08: 72 units

WLTC: 0 units


JC08: 4.9%

WLTC: 0.0%


humidity deviation

Not found 466 units

JC08: 39 units

WLTC: 427 units

0 units 0.0%
Failure to calibrate

emissions gas


Not found 5,310 units

JC08: 5,285 units

WLTC: 25 units

0 units 0.0%

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