kau83wi: Please provide your used Jenkins core and plugin version and if available the Jenkins system logs after restart. Probably you are missing some plugin dependencies, so have a look in the Jenkins plugin manager if there are some warnings. How did you install the plugin?

I have installed jenkins - 2.152 and Trace Tronic ECU Test Plugin 2.4 ; I faced some error with proxy: There were errors checking the update sites: IOException: Unable to tunnel through proxy. Proxy returns "HTTP/1.1 407 Proxy Authentication Required" which is still visible but on the other hand I am able to validate the proxy with a random test URL as well as I am able to download a plugin..

Dez 06, 2018 8:40:18 AM INFO org.eclipse.jetty.server.handler.ContextHandler doStart
Started w.@18162bc{Jenkins v2.152,/,file:///C:/Program%20Files%20(x86)/Jenkins/war/,AVAILABLE}

Dez 06, 2018 8:40:18 AM INFO org.eclipse.jetty.server.AbstractConnector doStart
Started ServerConnector@7e2ae7{HTTP/1.1,[http/1.1]}

Dez 06, 2018 8:40:18 AM INFO org.eclipse.jetty.server.Server doStart
Started @7479ms
Dez 06, 2018 8:40:18 AM INFO winstone.Logger logInternal
Winstone Servlet Engine v4.0 running: controlPort=disabled
Dez 06, 2018 8:40:21 AM INFO jenkins.InitReactorRunner$1 onAttained
Started initialization
Dez 06, 2018 8:40:21 AM INFO jenkins.InitReactorRunner$1 onAttained
Listed all plugins
Dez 06, 2018 8:40:26 AM INFO jenkins.InitReactorRunner$1 onAttained
Prepared all plugins
Dez 06, 2018 8:40:26 AM INFO jenkins.InitReactorRunner$1 onAttained
Started all plugins
Dez 06, 2018 8:40:28 AM INFO jenkins.InitReactorRunner$1 onAttained
Augmented all extensions
Dez 06, 2018 8:40:29 AM INFO jenkins.InitReactorRunner$1 onAttained
Loaded all jobs
Dez 06, 2018 8:40:29 AM INFO hudson.model.AsyncPeriodicWork$1 run
Started Download metadata
Dez 06, 2018 8:40:29 AM INFO jenkins.InitReactorRunner$1 onAttained
Completed initialization
Dez 06, 2018 8:40:29 AM INFO hudson.util.Retrier start
Attempt #1 to do the action check updates server
Dez 06, 2018 8:40:29 AM INFO hudson.WebAppMain$3 run
Jenkins is fully up and running
Dez 06, 2018 8:40:29 AM INFO hudson.util.Retrier start
The attempt #1 to do the action check updates server failed with an allowed exception: java.io.IOException: Unable to tunnel through proxy. Proxy returns "HTTP/1.1 407 Proxy Authentication Required" at sun.net.www.protocol.http.HttpURLConnection.doTunneling(Unknown Source) at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(Unknown Source) at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(Unknown Source) at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source) at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(Unknown Source) at hudson.model.DownloadService.loadJSON(DownloadService.java:167) at hudson.model.UpdateSite.updateDirectlyNow(UpdateSite.java:186) at hudson.PluginManager.checkUpdatesServer(PluginManager.java:1747) at hudson.util.Retrier.start(Retrier.java:62) at hudson.PluginManager.doCheckUpdatesServer(PluginManager.java:1718) at jenkins.model.DownloadSettings$DailyCheck.execute(DownloadSettings.java:130) at hudson.model.AsyncPeriodicWork$1.run(AsyncPeriodicWork.java:101) at java.lang.Thread.run(Unknown Source)
Dez 06, 2018 8:40:29 AM INFO hudson.util.Retrier start
Calling the listener of the allowed exception 'Unable to tunnel through proxy. Proxy returns "HTTP/1.1 407 Proxy Authentication Required"' at the attempt #1 to do the action check updates server
Dez 06, 2018 8:40:29 AM INFO hudson.util.Retrier start
Attempted the action check updates server for 1 time(s) with no success
Dez 06, 2018 8:40:29 AM SEVERE hudson.PluginManager doCheckUpdatesServer
Error checking update sites for 1 attempt(s). Last exception was: IOException: Unable to tunnel through proxy. Proxy returns "HTTP/1.1 407 Proxy Authentication Required"
Dez 06, 2018 8:40:29 AM INFO hudson.model.AsyncPeriodicWork$1 run
Finished Download metadata. 306 ms

Log indicates there´s no problem loading all plugins. Do you see the ECU-TEST plugin in the list of installed plugins in the Update Center? If successfully installed then their must be a category named ECU-TEST in the Global Tool Configuration at <Jenkins-URL>/configureTools/ and all provided build steps and publishers with prefix [TT] should be available.

There is no ECU-TEST section in Global Tool Configuration at <Jenkins-URL>/configure (That is the URL which opens when I click on the Global Tool Configuration). But, after your response i have enetred manually <Jenkins-URL>/configureTools/, and there I could find the section with ECU TEST. Thank you for the hint!