STEP/SEQUENCE RESULT WHAT TO DO NEXT TM 9-2320-363-20-1 Section 4 TROUBLESHOOTING CHARTS E.  FLASH CODE:   28 J1587 CODE: P172 4 - AIR TEMPERATURE CIRCUIT FAILED LOW (LOW VOLTAGE) NOTE - This chart is only to be used If: 1) All basic mechanical checks and physical inspections have been performed with no problem found, and 2) Diagnosis of DDEC-III was started at step Start-1, pg 3-345.41 and you have now been referred here. 28-1 Multiple Code Check Were there any other active No other codes. Go to 28-2. codes besides Code 172/4? Yes, any or all Go to ENG5V-1 (page 3-345.413). of the following codes: 110/3,175/3,174/3, 102/3, 72/3. Yes - but none Go to 28-2. of the above. 28.2 Sensor Check Turn ignition off. Code 172/3 (or any Go to 28-2. Disconnect ATS connector. other codes except Start engine and run until "Check Code 172/4). Engine" light comes on or for 8 minutes. Code 172/4 (and any Go to 28-4. Read active codes with engine other codes). still running. 28-3 Check ATS Connectors Inspect terminals at the ATS Terminals and Replace ATS.  Then go to connectors (both the sensor and connectors are okay. 28-30. harness side) for damage; bent, corroded, and unseated pins or Problem found. Repair terminals/connectors. sockets Then go to 28-30. 28.4 Check for Short Turn ignition off. Less than or Signal line (ckt#132) is  shorted Disconnect engine harness equal to 10,000 ohms to the return line (ckt#452) or connector at the ECM. on either reading. battery ground.  Repair short. Read resistance between sockets Then go to 28-30. N2 and Y2 on the engine harness connector. Greater than Go to 28-5. Also read resistance between 10,000 ohms or open socket B and a good ground. on both readings. Change 3  3-345.263