jonathan909 Posted July 22, 2015 Share Posted July 22, 2015 So far this one has been stumping us. EJ25 DOHC. Symptoms are bad/hard shifting and the AT OIL TEMP light flashing. No CEL or OBD codes. Did the shifter thing and got an error code 23 from the TCM - "AT LOAD SIGNAL", which goes from the ECM to the TCM. I followed the troubleshooting guide and confirmed the signal is out of range, and have checked the cabling and replaced the TCM, ECM, and MAF sensor (with junkyard parts). Nothing has changed the error or behaviour. Can anyone offer any suggestions? Thanks much. Quote Link to comment Share on other sites More sharing options...
Loyale 2.7 Turbo Posted July 22, 2015 Share Posted July 22, 2015 Have you noticed a sudden Drop of Readings or Lower Readings on the Speedometer and / or the Tachometer? I guess the ATF level is alright and has been properly measured; so the transmission might have an electrical false contact, a failing VSS (Vehicle Speed Sensor) or TSS (Turbine Speed Sensor) but not a complete fail yet, so I Kindly suggest you to start by checking and cleaning all the electrical contacts on the Transmission's wiring harness, and report if there is a change on the Behaviour. Kind Regards. Quote Link to comment Share on other sites More sharing options...
1 Lucky Texan Posted July 22, 2015 Share Posted July 22, 2015 any dents in the trans pan? stuff in there is easily damaged. Quote Link to comment Share on other sites More sharing options...
CNY_Dave Posted July 22, 2015 Share Posted July 22, 2015 What does the ECM use to determine what that signal should be? Whatever that sensor is could be faulty. Quote Link to comment Share on other sites More sharing options...
jonathan909 Posted July 22, 2015 Author Share Posted July 22, 2015 (edited) What does the ECM use to determine what that signal should be? Whatever that sensor is could be faulty. Well, kinda hard to tell, since I (we?) don't know exactly what "AT load signal" means. Presumably, any or all of the inputs available to the ECM. But if any of them (crank, cam, MAF, TPS, etc.) were faulty, it'd throw an OBD code, and that's not happening. The ECM seems to think everything is fine. Edit: See below - at the moment we think this may have to do with the MAP sensor, known in the '99 as the "boost sensor". Edited July 22, 2015 by jonathan909 Quote Link to comment Share on other sites More sharing options...
jonathan909 Posted July 22, 2015 Author Share Posted July 22, 2015 any dents in the trans pan? stuff in there is easily damaged. No dents. Full disclosure: I did a block swap last summer, but took pans to support the pan with a big chunk of 2"x8" so as to distribute the load. I'm aware of the potential for damage in there. Thing is, the car ran great after the motor work. Over the next couple of months we'd occasionally get the AT oil temp light blinking while out on the highway, but eventually it became a solid fault along with the bad/hard shifting. Quote Link to comment Share on other sites More sharing options...
jonathan909 Posted July 22, 2015 Author Share Posted July 22, 2015 Have you noticed a sudden Drop of Readings or Lower Readings on the Speedometer and / or the Tachometer? None such noted. I guess the ATF level is alright and has been properly measured; so the transmission might have an electrical false contact, a failing VSS (Vehicle Speed Sensor) or TSS (Turbine Speed Sensor) but not a complete fail yet, so I Kindly suggest you to start by checking and cleaning all the electrical contacts on the Transmission's wiring harness, and report if there is a change on the Behaviour. From what I can tell, if any of the (three) transmission speed sensors were bad, that'd be the blink-code the TCM would display. But we're not seeing any of that, just the code corresponding to this "AT load signal" from the ECM being bad. In fact, over the weekend (and misunderstanding - I think - the nature of the error message) I changed out the turbine speed sensor (for a junkyard part). Didn't make any difference. Since the voltage test on the ECM-to-TCM signal in question is indeed out of range, I'm pretty certain that the source of this fault lies in the upstream systems (the ECM and its sensors) and not in the TCM or transmission itself. At the moment we're looking at the MAP sensor - or its equivalent in the 1999 model, which is the "boost sensor" that's out on the shock tower next to the air filter. It's involved in a little conglomeration that includes two small air solenoid valves, one of which is mounted underneat the manifold. But that's just a guess, in part based on speculation that there's a typo in the 1999 diagnostic procedure... Quote Link to comment Share on other sites More sharing options...
Loyale 2.7 Turbo Posted July 22, 2015 Share Posted July 22, 2015 Understood. ...Thing is, the car ran great after the motor work. Over the next couple of months we'd occasionally get the AT oil temp light blinking while out on the highway, but eventually it became a solid fault along with the bad/hard shifting. So, maybe there is some electrical issue on the ECU wiring harness... Despite of the Lack of Codes, very kindly let me suggest you to Disconnect the Battery and keep it Disconnected at least for one Hour to discharge electricity from the Systems, some people also suggest to push the Brake pedal with battery disconnected to discharge any electricity that might been left saved on the condensers inside ECU and TCU; then reconnect the Battery and drive the Car, let us Know of there is a change on the shifting Behaviour / Blinking AT Temperature light issue. Kind Regards. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.