{"id":15256,"date":"2023-09-22T12:45:11","date_gmt":"2023-09-22T12:45:11","guid":{"rendered":"https:\/\/www.cnautotool.com\/blog\/?p=15256"},"modified":"2023-10-04T12:50:07","modified_gmt":"2023-10-04T12:50:07","slug":"8-vdc-supply-voltage-below-normal-diagnostic-code-spn-678-fmi-4","status":"publish","type":"post","link":"https:\/\/www.cnautotool.com\/blog\/8-vdc-supply-voltage-below-normal-diagnostic-code-spn-678-fmi-4\/","title":{"rendered":"8 VDC Supply Voltage Below Normal – Diagnostic Code SPN 678 – FMI 4"},"content":{"rendered":"

8 Volt DC Supply: Voltage Below Normal (CDL Code: 41-4)<\/strong><\/p>\n

\"\"<\/a><\/p>\n

Use this procedure to troubleshoot the electrical system if a problem is suspected with a sensor supply.
\n8 VDC Supply: Voltage Above Normal (CDL Code: 41-3)
\n8 VDC Supply: Voltage Below Normal (CDL Code: 41-4)
\n\u2192Comments: The Code is logged.<\/p>\n

#Probable Causes<\/strong>
\n\u2192Codes
\n\u2192Sensors
\n\u2192Sensor Supply Voltage<\/p>\n

#Recommended Actions<\/strong>
\nTroubleshooting Test Steps:
\n1). Check for Codes
\nA. Connect CAT Electronic Technician (ET) to the Service Tool\/ Diagnostic Port connector. Read More: How to Connecting Caterpillar ET Software to the ECM<\/a>.
\nB. Turn the keyswitch to ON.
\nC. Determine if a Diagnostic Trouble Code is present (SPN 678 – FMI 4), refer to Figure 1.1 above.
\nResults: A -3 or -4 code is present. Proceed to Test Step 2.
\n\"\"<\/a>
\n2). Check for a Failed Sensor
\nA. Disconnect a sensor on the suspect sensor supply circuit (Coolant Level Sensor).
\nB. Monitor CAT ET while the sensor is disconnected to see if the Active Code changes to logged.
\nResults:
\n\u2192The suspect sensor supply Active Code remains active after all sensors on the sensor supply circuit have been checked. Repair: A failed wiring harness has been detected. Repair or replace the wiring harness.
\n\u2192The suspect sensor supply Active Code changes to logged when a sensor is unplugged (refer to Figure 1.3 below). Repair: Replace the failed sensor.
\n\"\"<\/a>
\nC. Connect the suspect sensor to the wiring harness.
\nD. Repeat steps A through C for each sensor on the suspect sensor supply. If the problem is not resolved, proceed to Test Step 3.<\/p>\n

3). Check the Sensor Supply Voltage
\nA. Turn the keyswitch to OFF.
\nB. Unplug the suspect sensor from the wiring harness.
\nResults: A -4 code is activated on the suspect sensor supply. Repair: Remove the sensor. Check the sensor passage for a blockage or obstruction. Also, check for moisture frozen in the lines. If blockage is not found, replace the sensor.
\n\"\"<\/a>
\nC. Place a jumper wire between pin 1 and pin 2 on the suspect sensor wiring harness connector.
\nD. Connect to CAT ET.
\nE. Turn the keyswitch to ON.
\nF. Monitor the Diagnostic Codes using CAT ET<\/a>.
\nResults: A -4 code is not activated on the suspect sensor supply. Repair: The problem is in the wiring from the ECM to the sensor connector. Repair the wiring or replace the wiring.
\n\"\"<\/a><\/p>\n

https:\/\/www.cnautotool.com<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

8 Volt DC Supply: Voltage Below Normal (CDL Code: 41-4) Use this procedure to troubleshoot the electrical system if a problem is suspected with a sensor supply. 8 VDC Supply: Voltage Above Normal (CDL Code: 41-3) 8 VDC Supply: Voltage… Continue Reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":15259,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[2036,748],"tags":[103,1033,528,752,751,1096,1034,753],"_links":{"self":[{"href":"https:\/\/www.cnautotool.com\/blog\/wp-json\/wp\/v2\/posts\/15256"}],"collection":[{"href":"https:\/\/www.cnautotool.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.cnautotool.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.cnautotool.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.cnautotool.com\/blog\/wp-json\/wp\/v2\/comments?post=15256"}],"version-history":[{"count":2,"href":"https:\/\/www.cnautotool.com\/blog\/wp-json\/wp\/v2\/posts\/15256\/revisions"}],"predecessor-version":[{"id":15263,"href":"https:\/\/www.cnautotool.com\/blog\/wp-json\/wp\/v2\/posts\/15256\/revisions\/15263"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.cnautotool.com\/blog\/wp-json\/wp\/v2\/media\/15259"}],"wp:attachment":[{"href":"https:\/\/www.cnautotool.com\/blog\/wp-json\/wp\/v2\/media?parent=15256"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.cnautotool.com\/blog\/wp-json\/wp\/v2\/categories?post=15256"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.cnautotool.com\/blog\/wp-json\/wp\/v2\/tags?post=15256"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}