Join Date: Mar 2015
Location: Hythe. Kent. UK
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Need help with C121C Torque Request Denied Fault
I have a RHD 2008 JK fitted with a completely rebuilt 5.7 Hemi, a 545RFE and a JSS Hemi Kit.
The conversion was done last winter by a Pro from West Yorkshire as I live in the UK. I picked up the Jeep in January and it worked fine for few months.
Until around spring time this year when I was enjoying the huge Torque of that engine when taking over on the Motorway at around 75mph. All of a sudden it stopped pulling and went high in Revs as if the Transmission went into Neutral but it wasn't. So I released the accelerator and the Jeep started pulling again but soon after I realised the max speed I could go was about 60mph instead of the usual 85/90mph at same Revs when all was good.
I gradually noticed that the Transmission works but with lazy/late shifting but goes into every gear up to the 5th if I stay light on the accelerator but as soon as I want to take over or give it a bit of Revs the Trans goes down from 5th to 4th gear and never goes back to 5th anymore unless I stop and restart.
So after lots of online search I replaced the Transmission Solenoid pack as I heard that this part needs to be replaced when that Transmission gets around 70/80K Miles. Since I bought it second hand I thought that would cure the issue but it didn't.
I emailed Todd from JSS and he told me that my Transmission is old and I need to replace the Valve Body. The thing is if that was the case this issue would have occurred from day one but it has worked fine for about 4 months.
So I took the Jeep to an Auto-Trans Specialist. He kept the Jeep for a week, carried out all sorts of Tests and finally told me that there is nothing wrong with the Transmission. He said there is a Fault code: C121C "Torque Request Denied". He said the 5th gear in the 545RFE Transmission is only controlled by the ECU and until this fault is cleared the ECU will not send the command to go into 5th gear.
According to the Service Manual that fault is due to a break in the link between the ECU and the ABS.
I am struggling to find a good Auto Electrician this side of the Atlantic so I thought I would post my problem on here just in case this Fault has happened to someone else.