U1073: Engine Coolant Temp Data Missing
The U1073 code indicates that the Powertrain Control Module (PCM) or instrument cluster has detected invalid or missing engine coolant temperature data transmitted over the SCP (Standard Corporate Protocol) J1850 VPW communication bus. This communication failure prevents receiving modules from using coolant temperature for engine management strategies, fan control, or dashboard display.
1. Commonly Affected Makes
2. Most Common Causes
- Open circuit, short to ground/battery, or short between SCP+ and SCP- wires in the bus wiring
- Faulty PCM with corrupted software or internal failure
- Instrument cluster (HEC/IC) malfunctioning in reception or transmission
- Damaged or missing SCP bus termination resistors
- Electromagnetic interference (EMI) affecting the communication harness
3. Symptoms You Will Notice
- Check Engine Light illuminated
- Coolant temperature gauge reading incorrectly or stuck at zero
- Engine cooling fans running continuously or not at all
- Poor engine performance or reduced fuel economy
- Possible no-start condition in severe cases
4. Step-by-Step Diagnosis
Scan for additional codes and verify U1073 is present
Inspect SCP bus wiring for damage, corrosion, or shorts; check continuity between PCM and cluster
Test SCP bus termination resistors (typically 120 ohms each) at both ends of the bus
Monitor bus activity with a scan tool or oscilloscope to check for valid communication
If wiring and resistors are good, suspect PCM or instrument cluster failure; perform module self-tests or swap known-good modules
5. Frequently Asked Questions
Is it safe to drive?▼
Driving is not recommended because the PCM may use default coolant temperature values, leading to improper engine management, potential overheating, or poor performance. Have the vehicle diagnosed promptly.
How much does it cost to fix?▼
Repair costs vary widely: wiring repairs $100–$300, PCM replacement $500–$1,200, instrument cluster repair $200–$600, plus diagnostic fees. Total typically $200–$1,500.