P1794
CODE NUMBERScan tool: 58
General scan tool: P1794
CODE NAME
Speeds error: Speed sensor ground
CODE DESCRIPTION
Technical Description
The transmission system uses two speed sensors, one to measure input speed and one to measure output speed. These inputs are essential for proper transmission operation. Therefore, the integrity of this data is verified through the following checks:
1) When in gear, if the gear/speed ratio does not compare to a known gear ratio, the corresponding in-gear trouble code is set (codes 50 through 54).
2) An excessive change in input or output speeds indicating signal intermittency will result in codes 56 and/or 57 being set.
3) After a TCM reset in neutral, observing erratic output and input speeds indicating sensor signals indicates a loss of the common speed sensors ground. This set a code 58.
Check Area/Set Conditions
The transmission gear/speed ratio is monitored continuously while the transmission is in gear. This code is set if the gear/speed ratio is not correct for a period of time.
- Code 58 sets after a TCM reset in neutral and Nt/No equals a ratio of input to output of 2.50
Transmission Effects
The transmission will not go into relay open limp-in mode until three gear/speed ratio error events occur in a given key start. This allows for intermittent problems to correct themselves without opening the relay. However, if a gear/speed ratio error develops, a code is always set, but if the condition corrects itself the transmission will continue without requiring the ignition key to be cycled on and off. Many different events could occur given the range of failures possible for codes 50 through 58. The following are a few examples:
Codes 51, 52, 53, 54, 56, and 57 (at speeds below 35 km/h (22 mph) - If a gear/speed ratio problem is identified below 35 km/h (22 mph), the transmission will immediately substitute second gear for the current gear. If the gear/speed ratio problem goes away, normal operation will resume. If three gear/speed ratio problems are identified in a given key start, the transmission will go into relay limp-in mode.
Codes 51, 52, 53, 54, 56, and 57 (at speeds between 35 and 72 km/h (22-45 mph) - If one of these codes is set between 35 and 72 km/h (22-45 mph), the current gear will be maintained until the gear/speed ratio problem corrects itself. If throttle is applied, the transmission will go to 2nd gear. If this happens and the gear/speed ratio problem goes away, normal operation will resume. If three gear/speed ratio problems are identified in a given key start, the current gear will be frozen until throttle is applied. The transmission will then go into relay open limp-in mode with throttle applied at speeds between 35 and 72 km/h (22-45 mph).
Codes 51, 52, 53, 54, 56, and 57 (at speeds above 72 km/h (45 mph) - The appropriate code is set, EMCC is aborted and current gear is maintained. If while still traveling above 72 km/h (45 mph), the gear ratio becomes valid again, EMCC will reengage and normal operation will resume. If the gear ratio becomes intermittent and recovers three times in a given key start, the current gear will be maintained and EMCC inhibited, then the transmission will go into relay open limp-in mode if the throttle is applied below 72 km/h (45 mph) or at 35 km/h (22 mph) with closed throttle.
PROBABLE CAUSE
- Open or shorted speed sensor ground (speed ground is different from chassis ground).
- Open or shorted thermistor wiring to TRS.
- Defective transaxle range sensor - will also set code 74.
- Defective TCM.
DIAGNOSTIC CHART