The special feature of the 4 HP 16 automatic transaxle is that it operates without freewheels. Shifting between individual gears takes place by means of overlapping clutch engagement and release.
The advantages of overlap shifting are as follows:
| • | The transaxle can be of a more compact design and is lighter on account of the absence of freewheels and the lower number of shift elements. | 
| • | Lower drag losses, i.e. higher efficiency | 
| • | Lower peak torque acting on the components and driveline | 
However, overlap shifting necessitates high-performance hardware and software, and precision engine signals.
| • | The transmission oil temperature is greater than -10°C (+14°F). | 
| • | The selector lever is not in the neutral (N) or park (P) position. | 
| • | The system voltage is greater than 9 volts. | 
| • | No input speed error DTCs P0715, P0716, or P0717 are set. | 
| • | The output speed is greater than 256 RPM. | 
| • | The input speed is greater than 400 RPM. | 
| • | The 2-1 gear shift is active. | 
| • | The malfunction indicator lamp (MIL) will illuminate. | 
| • | The transmission control module (TCM) will record operating conditions at the time the diagnostic fails. This information will be stored in the Failure Records buffer. | 
| • | Adopt Emergency/Substitute mode and constant 3rd gear. | 
| • | Open lock up clutch | 
| • | The MIL lamp will turn OFF when the malfunction has not occurred after 3 ignition cycles. | 
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. | 
| • | Using a scan tool can clear history DTCs. | 
When DTC P1881 sets, the possible cause of the fault could be the TCM.
Step  | Action  | Value(s)  | Yes  | No  | 
|---|---|---|---|---|
1  | Did you perform the Diagnostic System Check - Automatic Transmission?  | --  | Go to Step 2  | |
2  | 
 Was a condition found?  | --  | Go to Diagnostic System Check - Engine Controls in Engine Controls  | Go to Step 3  | 
3  | Inspect the electronic control module (ECM). Was a condition found?  | --  | Go to Engine Control Module Replacement in Engine Controls  | Go to Step 4  | 
4  | 
 Is the voltage within the specified values?  | 11-14 V  | Go to Step 5  | |
5  | Replace the TCM. Refer to Transmission Control Module Replacement . Did you complete the replacement?  | --  | Go to Step 6  | --  | 
6  | 
 Has the last test failed or is the current DTC displayed?  | --  | Go to Step 7  | System OK  | 
7  | Replace the transaxle assembly. Refer to Transmission Replacement . Did you complete the replacement?  | --  | Go to Step 8  | --  | 
8  | 
 Are there any DTCs displayed that have not been diagnosed?  | --  | Go to Step 2  | System OK  |