The transmission control module (TCM) calculates gear ratio based on data from the automatic transmission input shaft speed (AT ISS) and automatic transmission output shaft speed (AT OSS) sensors. The TCM compares the calculated gear ratio to the known gear ratio for each commanded gear.
If the TCM detects an incorrect 1st gear ratio, indicating excessive slip or drag within the transmission, then DTC P0731 sets. DTC P0731 is a type A DTC.
This diagnostic procedure supports the following DTC:
DTC P0731 Incorrect 1st Gear Ratio
• | No TR switch DTC P0705. |
• | No transmission fluid temperature (TFT) DTCs P0711, P0712, or P0713. |
• | No ISS DTC P0717. |
• | No OSS DTC P0722. |
• | No engine speed DTC P0727. |
• | No solenoid DTCs P0962, P0963, P0966, P0967, P0970, P0971, P0973, P0974, P0976, P0977, P0979, P0980, P0982, P0983, P0985, or P0986. |
• | No engine torque DTC P1781. |
• | No throttle position DTC P1791. |
• | No controller area network (CAN) DTCs U2104 or U0100. |
• | The ignition voltage is 10.5-18 volts. |
• | The transmission temperature is greater than 20°C (68°F). |
• | Engine torque is between 30-200 N·m (22.13-147.51 lb ft). |
• | The transmission is in a forward range. |
• | The elapsed time since the most recent range change is 8 seconds or greater. |
• | The engine speed is at least 400 RPM and is at least 150 RPM greater than input shaft speed (ISS) for 0.5 seconds. |
• | The commanded gear has been 1st for 0.5 seconds or greater. |
• | The transmission input shaft speed (ISS) is 400 RPM or greater. |
• | The transmission output shaft speed (OSS) is 200 RPM or greater. |
The TCM commands 1st gear and the actual gear ratio is not within 3.75:1-5.62:1 for 10 seconds.
• | The TCM requests the powertrain control module (PCM) to illuminate the malfunction indicator lamp (MIL). |
• | Inhibit 1st gear. |
• | The line pressure is at maximum, and freezes the transmission adapt functions. |
• | Inhibit garage shift. |
• | The PCM records the operating conditions when the Condition for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records. |
• | The TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as a Failure Record. |
• | The TCM stores DTC P0731 in TCM history. |
• | The PCM turns off the MIL after the third consecutive drive trip in which the TCM does not send a MIL illumination request. |
• | A scan tool can clear the DTC. |
• | The TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without a non-emission related diagnostic fault occurring. |
• | The TCM cancels the DTC default actions when the ignition is OFF long enough in order to power down the TCM. |
Ask the customer about overloading the vehicle, or exceeding the trailer towing limit.
The numbers below refer to the step numbers on the diagnostic table.
This step determines that shift solenoid 4 or the U1 shift valve is stuck if the TCC applies in 2nd gear and stalls the engine.
This step determines if the output shaft speed sensor signal is skewed by a large factor.
This step determines if the input shaft speed sensor signal is skewed by a large factor.
This step determines that shift solenoid 2 or the M2 shift valve is stuck if the TCC Slip Speed is near 0 RPM at idle in DRIVE (D).
Step | Action | Values | Yes | No | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||||||||
2 | Inspect for correct transmission fluid level. Refer to Transmission Fluid Check . Is the transmission fluid level correct? | -- | Go to Step 4 | Go to Step 3 | ||||||||||
3 |
Did you find and correct the condition? | -- | Go to Step 25 | Go to Step 4 | ||||||||||
4 |
Important:
Is the 1st gear ratio within the specified range? | 3.75:1-5.62:1 | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 5 | ||||||||||
Drive the vehicle in 2nd gear. Does the engine stall when the transmission shifts into 2nd gear? | -- | Go to Step 14 | Go to Step 6 | |||||||||||
Is Transmission OSS parameter reading correctly? | -- | Go to Step 7 | Go to Step 19 | |||||||||||
Is Transmission input speed sensor (ISS) within the specified range? | 400-800 RPM | Go to Step 8 | Go to Step 18 | |||||||||||
Is TCC Slip Speed parameter within the specified range? | 0-100 RPM | Go to Step 13 | Go to Step 9 | |||||||||||
9 |
Does shift solenoid 1 click when commanded ON? | -- | Go to Step 10 | Go to Step 20 | ||||||||||
10 | Command shift solenoid 3 ON and OFF with a scan tool. Does shift solenoid 3 click when commanded ON and OFF? | -- | Go to Step 11 | Go to Step 21 | ||||||||||
11 | Perform a line pressure test. Refer to Line Pressure Check . Is the action complete? | -- | Go to Step 12 | -- | ||||||||||
12 |
Did you find excessive amounts of sediment? | -- | Go to Step 17 | Go to Step 15 | ||||||||||
13 | Inspect the control valve body assembly (39) for the following conditions:
Did you find any of the above conditions? | -- | Go to Step 22 | Go to Step 16 | ||||||||||
14 | Inspect the control valve body assembly (39) for the following conditions:
Did you find any of the above conditions? | -- | Go to Step 22 | Go to Step 16 | ||||||||||
15 | Inspect the control valve body assembly (39) for the following conditions:
Did you find any of the above conditions? | -- | Go to Step 22 | Go to Step 16 | ||||||||||
16 | Has the control valve body been serviced within the past 3 months or 4 828 km (3,000 mi)? | -- | Go to Step 17 | Go to Step 22 | ||||||||||
17 | Inspect the following items:
Is the action complete? | -- | Go to Step 23 | -- | ||||||||||
18 | Replace the input shaft speed sensor (73). Refer to Input Speed Sensor Replacement . Is the replacement complete? | -- | Go to Step 25 | -- | ||||||||||
19 | Replace the output shaft speed sensor (62). Refer to Output Speed Sensor Replacement . Is the replacement complete? | -- | Go to Step 25 | -- | ||||||||||
20 | Replace the reverse, 1st shift solenoid valve assembly (S1) - black (310). Is the replacement complete? | -- | Go to Step 25 | -- | ||||||||||
21 | Replace the 1-2, 2-3, reverse shift solenoid valve assembly (S3) - dark gray (300). Is the replacement complete? | -- | Go to Step 25 | -- | ||||||||||
22 | Repair or replace the control valve body assembly (39). Refer to Control Valve Body Cover Replacement . Is the action complete? | -- | Go to Step 24 | -- | ||||||||||
23 | Repair or replace the transmission. Refer to Transmission Replacement . Is the action complete? | -- | Go to Step 24 | -- | ||||||||||
24 |
Important: The Reset Trans Adapts function will clear all adapt cells. This may affect transmission performance. The TCM will update the adapt cell values as the vehicle is driven.
Did you complete the above procedures? | -- | Go to Step 25 | -- | ||||||||||
25 | Perform the following procedure in order to verify the repair:
Does the DTC reset? | -- | Go to Step 2 | Go to Step 26 | ||||||||||
26 | With the scan tool, observe the stored information, capture info and DTC info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK |