ZF8HP Ram 1500 Common Problems and Fixes

Since the 2013 model year, most automatic Ram 1500s have an eight-speed derived from the ZF 8HP behind the engine. That includes the DS trucks, the Ram 1500 Classic that kept the DS body, and the 2019-up DT. The complaints that bring them in are mostly software, the transmission heater, cooler line leaks, fluid level and age, and valve body wear, plus one 2023 recall. Most never need the transmission out of the truck.

Here is what each one looks like, what FCA, ZF and Sonnax actually published about it, and the order I work them in on a Ram.

Recommended ZF 8HP parts for the Ram 1500

A pan, filter and ATF service kit for the overdue fluid service and leak repairs, an 845RE valve body for 3.6L V6 trucks, and a remanufactured 8HP70 valve body with solenoids for Hemi trucks with worn bores. Match the part to your sales code. Secure checkout on our own site.

ZF 8HP70 Transmission Pan, Filter & ATF Kit RAM/Jeep/Dodge

$254.99View part

845RE ZF8HP45 Valve Body - Charger Challenger 300 RAM 3.6L

$413.99View part

8HP70 Valve Body with Solenoids, Remanufactured

$393.99View part

First: Which Eight-Speed Is in This Ram?

Do this before you order a part or apply a bulletin. FCA's own bulletins split the DS-generation trucks by sales code. Bulletin 21-037-15 lists the two units used in the 2015 Ram 1500: the 8HP70 (sales codes DFD or DFK) and the 845RE (sales code DFL). Bulletin 21-036-16 ties the 845RE to the 3.6L Pentastar V6 (engine sales code ERB), and bulletin 21-033-16 ties the 8HP70 to the 5.7L Hemi (engine sales code EZH). The 845RE is the Chrysler-built version of the lighter first-generation ZF 8HP45, so a V6 truck and a Hemi truck do not take the same valve body or hard parts.

The DT trucks use the second-generation units. FCA's 2024 safety recall 24V-413 names the 8HP75 in 2023 DT Ram 1500 trucks, and the 850RE is its V6 counterpart. Gen 1 and Gen 2 valve body parts do not interchange, so buy for the sales code or case tag, not a year range.

Problem 1: Shift Quality Complaints and False Codes Fixed by Software

On early DS trucks, a lot of what owners called a transmission problem was calibration, and FCA released TCM reflashes for both units.

845RE, 3.6L V6. Bulletin 21-036-16, which supersedes 21-025-15 Rev. A, covers 2015 Ram 1500 trucks with the 3.6L and the 845RE. It lists three DTCs that can set erroneously and turn on the MIL: P1DCD (TCM monitoring processor performance, multiple clutches locked up), P1B13 (Park-By-Wire unintended out of park position) and P0734 (gear 4 incorrect ratio). It also covers a bump felt during the engine start/stop transition on light throttle, poor downshifts in normal driving and when passing, and poor upshift quality in the lower gears. The 2016 revision adds a start/stop calibration change that lets Park and Neutral count as valid stop positions on trucks with the stop-start system.

8HP70, 5.7L Hemi. Bulletin 21-033-16 covers 2015 Hemi trucks with the 8HP70. Its changes are a shift schedule that expands the operating range of 8th gear and better 7th-gear upshift timing.

Two rules in these bulletins matter in any shop. First, put a battery charger on the truck: FCA says voltage must not drop below 13.2 volts or climb above 13.5 volts during the flash, and if the flash is interrupted it must be restarted. Second, 21-033-16 says do not clear the adaptation memory cells after the flash, because the transmission may not shift smoothly until the cells are fully relearned.

So when a DS truck shows up with a P0734, a P1DCD or a P1B13 and no driveability complaint to match, check the TCM software level before you condemn a clutch pack or a mechatronic. A real ratio code has a symptom you can feel and a ratio PID that drifts from the commanded gear.

Problem 2: Transmission Fluid in the Engine Coolant

The 8HP70 and 845RE in the Ram use a transmission heater, a coolant-to-ATF heat exchanger that warms the fluid faster on a cold start. When it fails internally, ATF and coolant mix. Bulletin 21-037-15 Rev. A, also released as Rapid Response Transmittal 15-062, covers 2015 Ram 1500 trucks built from December 1 to December 15, 2014 with either the 8HP70 or the 845RE. The symptom FCA lists is transmission fluid in the engine coolant.

The diagnosis is simple: read the build date label on the side of the heater assembly. If it falls between 2014-12-02 and 2014-12-09, the bulletin calls for replacing the heater with part number 52014750AD. If it falls outside that range, FCA says further diagnosis is required, including pressure testing the heater assembly. That last line is the important one for older trucks: a heater outside the build window can still leak, and the way to prove it is a pressure test, not a guess.

Do not stop at the heater. The bulletin says that if transmission fluid has been found in the engine coolant, the cooling system must be cleaned. Check the transmission side too. Coolant in the ATF turns it milky, and glycol is hard on clutch and converter friction material. FCA allows 1.6 hours to replace it on a 4x2 and 1.8 hours on a 4x4.

Problem 3: Leaks at the Cooler Lines

Cooler line leaks show up on both generations. On the DT, FCA released bulletin 21-019-23 (also Rapid Service Update 23-205) for 2023 Ram 1500 trucks built from December 1, 2022 through April 4, 2023 with the 3.6L eTorque V6 (sales code ERG) or the 6.2L supercharged Hemi (sales code ESD). The symptom is transmission fluid leaking toward the front of the truck. The cause is that the cooler lines were not fully seated into the transmission oil cooler, and the repair is to seat the lines and make sure the caps are fully seated too. FCA allows 0.2 hours to inspect and 0.6 hours to inspect and repair.

The bulletin is limited to trucks on the RSU VIN list, but the lesson applies to any Ram that has had the cooler or transmission out: a quick-connect line that looks connected may not be latched. Push it in, then pull back. On DS trucks, the same wet trail can come from the lines at either end or the heater connections. Clean it all, run it hot and trace the leak from the highest wet point down. Our ZF8HP cooler line replacement guide covers the line swap itself.

Problem 4: Wrong Fluid Level, Wrong Fluid, or Old Fluid

Any shift complaint on an 8HP starts with the fluid level, and there is no dipstick. The level is set at the fill plug with the fluid in a narrow temperature window, and a level set cold or set by feel will be wrong. ZF's Service Information 50130 for the 8HP oil change kit spells out the procedure. You need a scan tool that reads transmission oil temperature.

1. Truck level on the lift, selector in Park, parking brake on, lights and A/C and other loads off, and limp-home mode not active.
2. Start the engine and read transmission oil temperature. Below 30 C, let it warm up.
3. Between 30 and 50 C, hold 2,000 rpm for 30 seconds to fill the converter, then return to idle.
4. Select P, R and D, and hold D1 and D2 for about 10 seconds each. Recheck that the temperature is still 30 to 50 C.
5. Remove the fill plug. If fluid does not run out, add fluid until it does. Wait until only single drops come out, then install the plug.

ZF warns that too little fluid damages the transmission, and too much escapes through the overflow once it is hot. Do not set the level above 50 C. ZF lists two filler plug sizes for the 8HP: M18 x 1.5 with an 8 mm hex at 35 Nm, and M22 x 1.5 with a 10 mm hex at 30 Nm. Check which one is in the case and torque to match. For pans, ZF lists 10 Nm for the plastic pan with the integrated filter, tightened crosswise from the center out after every bolt is started by hand.

Fluid type and interval

FCA's own parts call-out in bulletin 21-019-23 is part number 68218925AB, with the note to use only Mopar ZF 8&9 Speed ATF or equivalent, because the wrong fluid may affect the function or performance of the transmission. ZF's equivalent is LifeguardFluid 8. ZF's LifeguardFluid 8 data sheet says these transmissions are generally filled with lifetime oil, and in the same document recommends an oil change after 150,000 km, about 93,000 miles, and sooner under high temperature, heavy load or unknown past use. ZF's oil change instructions also say no additives of any kind.

A drain and refill only replaces part of the fluid, since the converter and cooler keep a good share of it. Our ZF8HP fluid type and capacity guide has the full fill and interval discussion.

Problem 5: Valve Body Bore Wear on High-Mileage Trucks

When the software is current, the fluid is right and the complaint is still there, the valve body is the next stop on a high-mileage Gen 1 truck. Sonnax's ZF8HP45/ZF8HP70 valve body layout maps the common complaints to specific worn bores, and it matches what high-mileage Rams come in with:

• Bump shifts, flare shifts, burnt clutches, gear loss, and gear ratio or solenoid codes point at the clutch holding valve bores. Sonnax's oversized clutch holding valve kit, 35740-20K, covers five holding valve locations.
• Converter shudder, TCC slip, TCC codes and an overheated converter point at the TCC valve (ZF WK-V), kit 35740-13K.
• Coastdown clunk, harsh TCC apply, TCC codes and lining failure point at the TC pressure valve (ZF WD-V), kit 35740-18K.
• Harsh or soft shifts and erratic or high line pressure point at the pressure regulator valve (ZF SYS-DR), kit 35740-01K.

On the scan tool, watch commanded gear against the actual input-to-output speed ratio, and watch converter slip once lockup is commanded. A ratio that flares during the shift and then settles, warm, with clean fluid at the correct level, is a holding valve case. Steady converter slip in lockup that gets worse with heat points at the TCC side. A ratio code with burnt fluid and debris in the pan is not a valve body job: the unit comes apart. The bench test for these bores is in our ZF8HP valve body wear guide.

Problem 6: The 2023 8HP75 TCU Weld Recall

This one is small but serious. FCA recall 24V-413 covers about 214 2023 Ram trucks, including the DT Ram 1500, with the 8HP75. The control unit on the valve body may have been built with an insufficient weld between the cover and the baseplate. That can let transmission fluid reach the electronics, which can cause a loss of transmission control, including loss of motive power or the park function. The remedy is replacing the valve body. Run a VIN recall check on any 2023 DT with a sudden no-move or no-park before anything else.

The Order I Work a Ram 1500 Eight-Speed Complaint

1. Identify the unit: 845RE, 8HP70 or 8HP75, from the sales code or the case tag.
2. Run the VIN for open recalls and rapid response campaigns: 24V-413 on 2023 trucks, RRT 15-062 on early 2015 trucks, RSU 23-205 on early 2023 trucks.
3. Save all TCM and engine codes. Do not clear adaptations.
4. Check the TCM software level against the reflash bulletins. Flash with a charger on the truck.
5. Set the fluid level by the temperature-gated procedure. Look at the fluid: milky means the heater, dark and burnt means it has been abused.
6. If it was low, find the leak: cooler lines at both ends, heater connections, pan.
7. If the complaint is still there with correct, clean fluid, go to the valve body bores that match the symptom. Debris in the pan means a rebuild.

Frequently Asked Questions

What transmission is in a Ram 1500?

Most Ram 1500 trucks since 2013 use a ZF-based eight-speed. On the DS generation and the Classic, the 3.6L V6 uses the 845RE (sales code DFL) and the 5.7L Hemi uses the 8HP70 (sales code DFD or DFK). The 2019-up DT trucks use the second-generation units, including the 8HP75, so check the sales code before ordering parts.

Why is there transmission fluid in my Ram 1500 coolant?

The transmission heater, a coolant-to-ATF heat exchanger, can leak internally. FCA bulletin 21-037-15 covers 2015 trucks built December 1-15, 2014, and calls for replacing the heater with part 52014750AD if its build date is 2014-12-02 to 2014-12-09. Outside that range FCA calls for pressure testing the heater, and the cooling system must be cleaned whenever ATF is found in the coolant.

What transmission fluid does a Ram 1500 8-speed take?

FCA specifies Mopar ZF 8&9 Speed ATF, part number 68218925AB, or an equivalent, and warns the wrong fluid may affect how the transmission works. ZF LifeguardFluid 8 is the ZF equivalent. ZF recommends a change at 150,000 km, about 93,000 miles, and sooner for towing, heat or unknown history.

Should I reset the transmission adaptations on my Ram 1500?

Not as a first step. FCA's 8HP70 reflash bulletin 21-033-16 says not to clear the adaptation memory cells after the flash, because the transmission may not shift smoothly until they are fully relearned. Check codes, software level and fluid level first.