IAT Rationality Test
The IAT rationality test determines if the IAT sensor is producing an erroneous temperature indication within the normal range of IAT sensor input.
The IAT sensor rationality test is run only once per power-up. The IAT sensor input is compared to the CHT sensor input (ECT sensor input on some applications) at key-on after a long (6 hour) soak. If the IAT sensor input and the CHT (ECT) sensor input agree within a tolerance (+/- 30 deg F), no malfunction is indicated and the test is complete. If the IAT sensor input and the CHT (ECT) sensor input differ by more than the tolerance, the vehicle must be driven over 35 mph for 5 minutes to confirm the fault. This is intended to address noise factors like sun load that can cause the IAT sensor to indicate a much higher temperature than the CHT (ECT) sensor after a long soak. Driving the vehicle attempts to bring the IAT sensor reading within the test tolerance. If the IAT sensor input remains outside of the tolerance after the vehicle drive conditions have been met, the test indicates a malfunction and the test is complete.
In addition to the start-up rationality check, an IAT "Out of Range" check is also performed. The test continuously, checks to see if IAT is greater than the "IAT Out of Range High threshold", approximately 150 deg F. In order to prevent setting false DTC during extreme ambient or vehicle soak conditions, the same count up/count down timer used for the IAT startup rationality test is used to validate the fault. If IAT is greater than 150 deg F and vehicle speed is greater than ~ 40 mph for 250 seconds then set a P0111.
Either the IAT startup rationality test or the IAT Out of Range High test can set a P0111 DTC. The logic is designed so that either fault can trigger a "two-in-a-row" P0111 MIL, however, both faults must be OK before the P0111 DTC is cleared.
Block heater detection results in a no-call.
INTAKE AIR TEMPERATURE SENSOR RANGE/PERFORMANCE CHECK OPERATION
| DTCs |
P0111 (range/performance) |
| Monitor execution |
Once per driving cycle, at start-up |
| Monitor Sequence |
None |
| Sensors OK |
ECT/CHT, IAT, VSS |
| Monitoring Duration |
Immediate or up to 30 minutes to register a malfunction |
TYPICAL INTAKE AIR TEMPERATURE SENSOR RANGE/PERFORMANCE ENTRY CONDITIONS
| Entry condition |
Minimum |
Maximum |
| Engine off (soak) time |
6 hours |
|
| Battery Voltage |
11.0 Volts |
|
| Time since engine start (if driving req'd) |
|
30 min |
| Vehicle speed (if driving req'd) |
40 mph |
|
| Time above minimum vehicle speed (if driving req'd) |
5 min |
|
| IAT - ECT at start (block heater inferred) |
-30 °F |
-90 °F |
TYPICAL IAT SENSOR CHECK MALFUNCTION THRESHOLDS
| IAT and ECT/CHT error at start-up > +/-30 deg F |
INTAKE AIR TEMPERATURE SENSOR OUT OF RANGE HIGH CHECK OPERATION
| DTCs |
P0111 (Out of Range High) |
| Monitor execution |
Continuous |
| Monitor Sequence |
None |
| Sensors OK |
ECT/CHT, IAT, VSS |
| Monitoring Duration |
250 seconds to register a malfunction |
TYPICAL INTAKE AIR TEMPERATURE SENSOR OUT OF RANGE HIGH ENTRY CONDITIONS
| Entry Condition |
Minimum |
Maximum |
| Engine off (soak) time |
6 hours |
|
| Battery Voltage |
11.0 Volts |
|
| Vehicle speed |
40 mph |
|
| Time above minimum vehicle speed (if driving req'd) |
5 min |
|
TYPICAL IAT SENSOR OUT OF RANGE HIGH CHECK MALFUNCTION THRESHOLDS